10L1000 vs Allison 1000: Differences, Ratios, and Which Is Stronger

Every week somebody calls about a 2020-or-later Duramax and calls the transmission "the Allison." They are half right. The badge on the fender still says Allison, but the unit under a 2020-up Silverado or Sierra 2500/3500 HD is the 10L1000 ten-speed, not the Allison 1000 six-speed that rode behind the Duramax for two decades. Different case, different clutches, different fluid, different failure patterns, and almost nothing interchanges.

This guide puts the two side by side the way they come across the bench: where each one was used, how they are built, the ratios, the fluid and fill, what fails, and how to diagnose each. Every spec here comes from Chevrolet, GM TechLink, GM service bulletins, Allison and GEARS Magazine documents listed at the bottom.

Recommended 10L1000 and Allison 1000 parts

Order by unit, nothing crosses between them: a DEXRON ULV service kit and a filter and pan gasket kit for the 10L1000, and TranSynd 668 for an Allison 1000 fluid service. Secure checkout on our site.

10L1000 Transmission Service Kit with Fluid and Filters

$281.99View part

10L1000 Transmission Filter and Pan Gasket Kit, L5P Duramax

$78.99View part

Castrol TranSynd 668 Synthetic Automatic Transmission Fluid, 1 Gallon

$59.99View part

The Short Answer

10L1000: ten forward speeds from four planetary gearsets and six clutches, introduced for 2020 behind the 6.6L Duramax and made standard behind the 6.6L gas V8 for 2024, DEXRON ULV, 13.6 L / 14.4 qt [1][2][3]. Allison 1000: six forward speeds with wide steps, the Duramax pickup transmission through 2019, Allison TES 295 / TES 668 approved fluids, and it is still listed in GM's 2026 chart in the Low Cab Forward medium-duty truck [3][4][7].

They do not share fluid, filters, valve bodies, clutch packs or a TCM strategy. Identify which one you have before you order anything.

Where Each One Lives

Allison 1000 (LCT1000, RPO MW7)

The Allison 1000 is the six-speed that built the "Duramax-Allison" reputation. GM's 2016 Silverado HD spec sheet lists it behind the 6.6L Duramax, rated at 765 lb-ft at 1600 rpm, while the gas 6.0L in the same truck got the 6L90 [4]. That split held until the 10-speed arrived. In GM's 2026 capacities chart the Allison 1000 (RPO MW7) is still there, but only in the Low Cab Forward medium-duty truck [3].

10L1000 (RPOs MGM, MGU, MKM)

GM TechLink introduced the 10L1000 as the transmission for the 2020 Silverado HD and Sierra HD with the 6.6L Duramax, RPOs MGM and MGU [2]. GEARS Magazine's Steve Garrett puts it plainly: the 10L1000 replaced the Allison LCT 1000 for 2020 [5]. For 2024 Chevrolet made the Allison-branded ten-speed standard with both HD engines, the 401 hp / 464 lb-ft 6.6L gas V8 and the 470 hp / 975 lb-ft Duramax, and said outright that it replaced the gas engine's previous six-speed [1]. The gas-engine version is RPO MKM; GM bulletin 24-NA-148 spells out MKM = 6.6L L8T gas, MGM/MGU = 6.6L L5P diesel [6].

So the quick decoder for a GM HD pickup: 2001-2019 Duramax = Allison 1000; 2020-up Duramax = 10L1000; 2020-2023 gas = six-speed (not an Allison); 2024-up gas = 10L1000. Pull the RPO sticker in the glovebox or the build data to confirm. The MGU code is the PTO version [2].

Architecture Side by Side

10L1000

GM TechLink describes ten forward ratios and one reverse from four simple planetary gearsets, two brake clutches and four rotating clutches. The four rotating clutches sit forward of the gearsets to shorten the oil feeds, the case has an integral bellhousing for stiffness, and the pump is an off-axis, gear-driven variable-vane pump located in the valve body. There are two control valve body assemblies, an externally mounted TCM fed by three speed sensors, and a 4-element converter with a pressure plate splined to the turbine [2].

Electrically it runs up to nine solenoids depending on RPO: solenoids 1 through 8 are pressure-regulating and the ninth is on/off, with normal operating current of 0 to 1.2 amps. The pressure-regulating solenoids have a performance data file stored in the TCM and on TIS [2]. That matters at the counter: replace the lower valve body with solenoids, or one solenoid, and the new file has to be programmed. Replace the TCM and you program the existing file [2]. Skip that step and you are chasing shift quality you created.

Size is the other difference people underestimate. GEARS notes it looks a lot like a 10L80 but is much larger and weighs over 360 pounds, and on 4WD trucks the transfer case has to be tipped about 60-70 degrees to clear the output shaft because the crossmember stays in place. Garrett's advice is to get a second person for that job [5].

Allison 1000

The Allison is a simpler mechanical layout: six forward speeds with wide ratio steps, a removable valve body on the bottom of the case, a spin-on external filter plus an internal filter, and a prognostics system in the TCM that tracks fluid life and filter life. Allison's operator manual ties prognostics to approved fluid and Control Main Filter P/N 29539579 [7]. If somebody runs non-approved fluid or a generic filter, the prognostics readings are not valid.

Gear Ratios

10L1000 [1]: 4.54, 2.87, 2.06, 1.72, 1.48, 1.26, 1.00, 0.85, 0.69, 0.63, reverse 4.54. Final drive 3.73 with the 6.6L gas, 3.42 with the Duramax.

Allison 1000 [4]: 3.10, 1.81, 1.41, 1.00, 0.71, 0.61, reverse 4.49.

The ten-speed starts much deeper (4.54 vs 3.10) and finishes at nearly the same overdrive (0.63 vs 0.61). Chevrolet's stated reason for putting it behind the gas engine was the smaller steps, which keep a gas V8 that makes peak torque at 4000 rpm closer to its power, plus better grade braking from the closer ratios [1]. A diesel with 975 lb-ft at 1600 rpm does not need ten gears to stay in its band, but the deep first gear helps launching a heavy trailer and the closer steps keep exhaust temps and rpm down on a grade.

For a tech, more gears means more clutch-to-clutch shifts under load. On the ten-speed, a slipping clutch typically shows as a ratio error in the specific gears that use it. On the Allison, the complaint is usually a flare on one specific upshift.

Clutch Application: Know Which Clutch You Are Chasing

GEARS lists the 10L1000 clutches by the gears they are applied in, which is the fastest way to work out which clutch a gear-specific slip points to [5]:

• 1-2-8-9-10-R clutch
• 1-2-3-4-5-6-R clutch
• 2-3-4-5-7-9-10 clutch
• 1-2-3-4-6-7-8-10-R clutch (GM calls this C4 in bulletin 24-NA-148) [6]
• 4-5-6-7-8-9-10-R clutch (GM calls this C6 in 24-NA-148) [6]
• 1-3-5-6-7-8-9 clutch
• PTO clutch, on PTO-equipped cases only

Non-PTO units have six clutches; PTO units have a different case with the PTO and its clutch housed in the offset section, for seven [5]. Four clutches are applied in any one gear [5]. Use the clutch names, not the C-numbers, when you compare documents. The numbering is not consistent across sources, but the gear lists are.

Fluid, Capacity and Level

10L1000

GM's 2026 TechLink chart lists all three 10L1000 RPOs (MKM, MGM, MGU) in the Silverado and Sierra 2500/3500 HD at 13.6 L / 14.4 qt of DEXRON ULV [3]. ULV is GM's low-viscosity fluid for the ten-speeds and it is not a substitute for, or a substitute with, the Allison fluids below. A pan and filter service does not drain the full 14.4 qt, so fill by the hot level check procedure in service information, not by what came out of the pan.

Allison 1000

Allison approves TES 295, TES 668 and TES 389 fluids for the 1000 Series, and GM's 2026 chart lists the Allison 1000 (MW7) at 12.8 L / 13.5 qt with TES-295 or TES-668 [3][7]. The hot level check is valid at a normal sump temperature of 71-93 C (160-200 F) [7]. A cold check on an Allison is how a truck gets overfilled, aerates the fluid, and comes back with a shift complaint.

Service Intervals

Allison publishes an interval table in operator manual OM8471EN (Table 6-2). With TES 668 or TES 295 fluid: 150,000 miles / 48 months for general duty, 75,000 miles / 36 months for severe duty. With TES 389 fluid the general interval drops to 50,000 miles / 24 months [7]. A truck that tows for a living is severe duty.

The 10L1000 does not use the Allison prognostics table. In our shop a 10L1000 that tows a fifth wheel or a gooseneck gets treated as severe service: pan, filter and ULV refilled to the hot level well before 75,000 miles. ULV is thin by design, and there is not much margin left once it has been cooked.

Known Weak Spots

10L1000: the 1-3-5-6-7-8-9 clutch

GEARS reports that when shops see a clutch failure in this unit it is typically the 1-3-5-6-7-8-9 clutch. It is a rotating clutch tied to the input shaft and housed in a drum, with a backing plate built into a support. Garrett's point is that the integral backing plate does not fully support the clutch pack, the pack flexes, and the clutch burns. The aftermarket picked up on it early, so ask your supplier for the updated components when you are in there [5].

10L1000 gas (MKM): C4 piston seal and C6 piston, bulletin 24-NA-148

For 2024 Silverado and Sierra 2500/3500 HD trucks with the 6.6L L8T gas engine and 10L1000 (MKM), GM bulletin 24-NA-148 covers slip, harsh 3-4 or 5-6 shifts, delayed shifts, delayed or harsh reverse, slipping in reverse or no reverse, and a MIL with DTC P2714 (solenoid 4 stuck off) and/or P2732 (solenoid 6 stuck off) [6]. The bulletin states it does not apply to the MGM/MGU diesel units.

The cause GM gives: the C4 apply piston outer seal degrades prematurely because of the machine finish on the seal contact area of the triple clutch housing. A good seal has an orange stripe; a degraded one is all black. The C6 apply piston may also show a de-bond or tear. GM notes that the pan often shows little or no clutch sediment and that replacing the valve body does not fix it. The correction is the triple clutch housing, C4 apply piston, C4 outer seal and C6 apply piston [6].

That last point is the one that saves money. A P2714 or P2732 on one of these trucks reads like a solenoid code, but per the bulletin it is a mechanical sealing problem inside the clutch housing. Check the bulletin against the VIN and RPO before you sell a valve body.

Allison 1000

The six-speed's complaints are older and well documented: shift flare from worn valve body bores and solenoid regulator valves, TCC shudder on high-mileage towing trucks, and problems caused by wrong fluid or a skipped filter service. These units also respond badly to a level checked cold or outside the 160-200 F window [7]. Our Allison 1000 valve body testing guide covers the bench side of that.

Diagnosis Notes for Either Unit

Confirm the transmission first. Model year and engine get you most of the way (see the decoder above), but the RPO code settles it. A 2020-up diesel quote built around Allison 1000 parts is wrong from the start.

10L1000: read the commanded gear against the calculated ratio, and note which gears slip. Match the slipping gears against the clutch list above. If every slipping gear shares one clutch, you have found your suspect before the pan comes off. Then check bulletins by RPO: MKM gas trucks with P2714/P2732 and 3-4, 5-6 or reverse complaints point to 24-NA-148 [6]. Any solenoid or lower valve body replacement requires programming the new performance data file [2].

Allison 1000: check level hot (160-200 F), verify the fluid is an approved TES type, read the prognostics, and find out when the filters were last changed [7]. A flare on one upshift with correct fluid and level usually leads you to the valve body.

Which One Is Stronger?

On paper the 10L1000 is carrying more. Chevrolet rates the 2024 Duramax at 975 lb-ft and put the ten-speed behind it, against the 765 lb-ft Duramax rating the Allison 1000 carried in GM's 2016 HD specs [1][4]. The ten-speed also gives a deeper first gear and better grade braking [1]. The Allison 1000 has the longer track record, a simpler mechanical layout, a published interval table, and twenty years of aftermarket parts behind it [7].

In practice they are not competing for the same truck. If you own a 2020-up HD, you have a 10L1000, and the question is how to keep it alive: correct ULV level, severe-duty service if you tow, and know the clutch and bulletin history. If you own a 2001-2019 Duramax, the Allison 1000 is a known quantity that rewards correct fluid and filters.

FAQ

Is the 10L1000 an Allison transmission?

It carries Allison branding and GM TechLink calls it the Allison 10-speed, but it is a different transmission from the Allison 1000 six-speed. GEARS Magazine notes the 10L1000 replaced the Allison LCT 1000 in 2020 HD trucks, and it shares no fluid, filters, valve body or clutch packs with the six-speed.

Which GM HD trucks have the 10L1000 and which have the Allison 1000?

2001-2019 Duramax Silverado and Sierra HD trucks use the Allison 1000 six-speed. 2020-and-later Duramax trucks use the 10L1000 (RPO MGM or MGU), and for 2024 Chevrolet made the 10-speed standard behind the 6.6L gas V8 as well (RPO MKM), replacing the previous six-speed. Check the RPO code on the glovebox label to confirm.

What fluid and how much does the 10L1000 take compared with the Allison 1000?

GM's 2026 TechLink chart lists the 10L1000 at 13.6 liters (14.4 quarts) of DEXRON ULV. The Allison 1000 takes Allison-approved TES 295 or TES 668 fluid, listed by GM at 12.8 liters (13.5 quarts) in the Low Cab Forward, and Allison also approves TES 389. The fluids are not interchangeable.

Is the 10L1000 stronger than the Allison 1000?

On paper it carries more: Chevrolet put the 10L1000 behind the 2024 Duramax rated at 975 lb-ft, while GM's 2016 HD specs list the Allison 1000 behind a 765 lb-ft Duramax. The Allison 1000 has a longer track record and a simpler layout; the 10L1000 has known issues such as the 1-3-5-6-7-8-9 clutch reported by GEARS and the C4 seal problem in GM bulletin 24-NA-148 on 2024 gas trucks.

Will replacing the valve body fix a 10L1000 P2714 or P2732?

On 2024 HD trucks with the 6.6L gas engine and 10L1000 (RPO MKM), GM bulletin 24-NA-148 says no. The bulletin traces those codes, along with slipping and harsh 3-4, 5-6 or reverse shifts, to a degraded C4 apply piston outer seal caused by the triple clutch housing's machine finish, and states valve body replacement does not resolve it.