6L90 Silverado 2500 Common Problems and Fixes

The gas Silverado 2500HD is the hardest job GM ever gave the 6L90. Same six-speed family that sits behind a half-ton 5.3, but bolted to a 6.0L Vortec in a truck rated to pull 14,500 lb on a ball hitch, usually with a work trailer or a camper behind it. When these trucks come in, the complaints repeat: a shudder at 30-40 mph, heat on a long grade, a slow or missing Reverse on the early trucks, and the rebuilt unit that comes back burnt a month later. This guide walks through each one with the GM bulletin that covers it and the gauge or scan reading that confirms it.

For the 6L90 across every vehicle (vans, Suburbans, half-tons), start with 6L90 common problems and fixes. This page stays on the 2500HD gas truck and what is different about it.

Recommended 6L90 parts

Matched to the problems below: a master rebuild kit for burnt clutch packs, the Sonnax TCC regulator valve kit for worn-bore shudder and harsh lockup, and a cooler bypass kit for the heat a towing 2500HD makes. Secure checkout.

6L90 Master Rebuild Kit

$314.99View part

Sonnax 6L45/6L50/6L80/6L90 TCC Regulator Valve Kit 104740-46K

$91.99View part

Superior STL010 Sure Cool Cooler Bypass Upgrade Kit for GM 6L80 / 6L90 / 8L90

$71.99View part

Which 2500HD Trucks Have the 6L90

Read the RPO codes on the glove box label. You want MYD, the 6L90. GM's 2016 Silverado HD specification sheet lists two automatics: the Hydra-Matic 6L90 with the Vortec 6.0L (L96 / LC8 bi-fuel) and the Allison 1000 with the Duramax 6.6L. If your truck is a diesel, nothing on this page applies; it has an Allison.

The 6L90 showed up in the HD gas trucks with the 2007 GMT900 redesign. GM's housing weld bulletin 09-07-30-004J lists 2007-2008 Silverado and Sierra with the 6L80 or 6L90, and GEARS Magazine documented a 2007 GMC K2500 6L90E on the bench. It stayed through 2019 with the 6.0L, and GM's thermal bypass valve bulletin 21-NA-199 still lists the 2020-2021 Silverado 2500HD/3500HD under RPOs MYC/MYD, which covers the 6.6L gas trucks that followed.

Ratios and towing are from GM's 2016 HD spec sheet; the fluid and the 6.0 qt service capacity are from GM TechLink's transmission capacity table for RPO MYD. Six quarts is a pan drop, not a dry fill. Set the final level at the check plug with the fluid in the service temperature window.

Problem 1: Surge or Shudder at 30-40 MPH

This is the top complaint on 2016-2019 trucks, and the first thing to know is that some of it is designed in. GM bulletin 18-NA-253 covers 2016-2019 Silverado and Sierra (including the 2019 2500/3500), Express and Savana with the 6.0L L96 and RPO MYD. Customers describe surge, chuggle, misfire, fishbite or shudder at a steady 30-40 mph with light throttle and the TCC applied.

GM's cause: a reduced TCC slip calibration meant to reduce converter wear under heavy load, which lets engine combustion instability at low rpm and high load reach the cab. The diagnosis is a scan tool, not a guess:

• Watch TCC slip speed on a test drive at 30-40 mph. Steady between roughly 0 and 20 rpm is the condition GM describes.
• If slip climbs, drops back to 0 and starts cycling, that is real TCC shudder, and GM sends you to PIP 5504F.
• Check for misfire counts at the same time. Misfires go to engine diagnostics.

Steady slip and no misfires: GM says the condition is characteristic of the vehicle and no repair should be made. Tell the customer that before you sell them a converter they do not need.

When it really is the converter

If slip is cycling, look at the fluid and the mileage. GM bulletin 20-NA-142 covers 6L80/6L90 trucks including the Silverado 2500/3500 and traces surging and converter shudder to depleted fluid additives that help regulate clutch slip. Its triple drain-and-fill with DEXRON VI applies only at 30,000 miles or less. Over 30,000 miles, GM's instruction is to replace the torque converter and the transmission filter.

A shudder that comes with harsh shifts, hot fluid or a P0741/P0742 points at the TCC regulator valve bore. Sonnax lists bore wear there as a cause of no TCC apply or slip on engagement, harsh shifts, overheated fluid, failsafe mode and high TCC slip rpm. A valve stuck in apply gives a harsh lockup; stuck in release gives no lockup or slip. On a high-mileage tow truck, ream and fit the oversized valve kit (Sonnax 104740-46K) whenever the valve body is apart. More in our 6L90 torque converter shudder guide.

Problem 2: Heat, Harsh Shifts and a Twisted Cooler Line

A 2500HD with a trailer behind it makes heat for a living, so cooling problems show up here first. GM bulletin 22-NA-182 (it replaced PIP5792E) covers the 6L80, 6L90, 8L90 and 10-speeds with harsh shifting, shudder, surging, stalling, neutral/flare and overheating. On low-mileage trucks GM's cause is a twisted rubber cooler line at the auxiliary cooler. You may need to pull the underbody panels to see it. Untwist it, replace it if it stays misshapen, and recheck the fluid level.

If the lines are good, GM points to the thermal bypass valve. On the 6-speeds the TBV is external to the transmission and opens at 158 F (70 C). Bulletin 21-NA-199 released an updated TBV stamped "70" on the bottom of the valve, fully open at 158 F instead of the old valve's 194 F. For the Silverado and Sierra 2500HD/3500HD, GM lists part number 85547828. GM says it should be replaced once during any transmission repair, including a "concern not duplicated" visit, and it lists harsh shifts, slip, surge, shudder, delayed shifts and noise as conditions. Look at the valve. No "70" stamp means it has not been done.

The 2019 HD owner manual puts transmission fluid temperature on the driver information center, so there is no excuse not to watch it. A truck that runs hot on every grade with a good TBV and clean cooler needs more cooler, not a fresh fill. Our 6L90 towing upgrades page covers cooler bypass kits and the valve body work that helps under load.

Problem 3: Slow or No Reverse on 2007-2008 Trucks

GM bulletin 09-07-30-004J covers 2007-2008 Silverado and Sierra with the 6L80 or 6L90. The condition list: slip or no Reverse, delayed Reverse engagement, MIL with P0776, P2715 or P2723, harsh 2-3, harsh 4-5 or slip in 5th, and slipping when passing.

The cause on 2006-2008 units is a cracked weld on the 1-2-3-4 / 3-5-R clutch housing. The test works with the housing assembled or apart: soap on the weld, thumb over the air bleed passage, air into the 3-5R clutch feed hole, and watch for bubbles. Bubbles mean a new housing. GM notes complete assembled housings are available with pistons, seals and clutches installed. A truck that started with a lazy Reverse and a harsh 2-3 and now will not back a trailer up a driveway has followed this bulletin start to finish. See 6L90 no reverse fix for the rest of the Reverse list.

Problem 4: The Rebuild That Comes Back Burnt

This one gets shops in trouble on HD trucks. GEARS Magazine (Pete Huscher, May 2016) wrote up a 2007 GMC K2500 6L90E that came back a month after a rebuild with burnt fluid. Line pressure held at 65-70 psi with no rise on acceleration, and unplugging the transmission connector to force maximum line rise still topped out near 70 psi. The 1-2-3-4, 3-5-R and 4-5-6 packs were burnt. The previous rebuilder had installed a new OEM torque converter housing, and the new housing was an updated design. The pump body was the old design, and GM's parts department confirmed the two had to be replaced as a matched set. A matching pump body fixed it.

Sonnax's no-movement analysis for the 6L80/90 describes the same gauge picture from a different cause: line pressure near 60-68 psi with no rise points at the TEHCM line pressure control solenoid stuck in exhaust, and unplugging it gives the same reading. Under about 30 psi at idle points at a missing pressure regulator boost valve retaining pin in the pump. The lesson for an HD truck is simple: put a line pressure gauge on every rebuild before it leaves, and confirm pressure rises with throttle. Five minutes on a gauge is cheaper than a second set of clutches.

Problem 5: Slipping and No Forward

Slipping forward or falling out of gear cold, sometimes with P2723 or P2724 and sometimes with no code, often comes from the No. 1 check ball in the upper valve body. GEARS Magazine (Steve Garrett) describes the ball wearing from 0.250 in. down to 0.180 in. or less until it sticks in or blows through the spacer plate. The 1-2-3-4 clutch then cannot apply. Check that ball before you order a TEHCM or tear down for the low one-way clutch, and replace every check ball when the valve body is apart. Sonnax adds two HD-specific traps: a 6L90 valve body installed on a 6L80 causes no Reverse, and the wrong separator plate for the valve body type gives no Forward or no 3rd and Reverse. Full walkthrough in 6L90 slipping causes and fix.

Keeping a Work Truck's 6L90 Alive

• Use Tow/Haul with a trailer. GM says it reduces shift cycling and improves transmission cooling.
• DEXRON VI only, and service it on the severe schedule if it tows. Do not wait for a shudder.
• Replace the filter seal with the filter. GM bulletin 23-NA-224 split filter 24236517 and seal 24225347 into separate part numbers. Order both.
• Confirm the "70" TBV any time the truck is in for transmission work.
• On a rebuild, match the pump body to the converter housing, replace the check balls, and gauge line pressure before delivery.

FAQ

What are the most common problems with the 6L90 in a Silverado 2500HD?

On the gas 2500HD the repeat complaints are a surge or shudder at 30-40 mph with the converter locked, overheating and harsh shifts when towing, slow or no Reverse on 2007-2008 trucks, and rebuilt units that come back burnt from low line pressure. Each has a GM bulletin or a published tech article behind it, and most can be confirmed with a scan tool or a line pressure gauge before any parts are ordered.

Is the 30-40 mph shudder in my 6.0L Silverado 2500 normal?

It can be. GM bulletin 18-NA-253 says a chuggle at steady 30-40 mph with the TCC applied and slip steady between about 0 and 20 rpm comes from a converter-protecting calibration and needs no repair. If TCC slip cycles up and back to zero, that is true shudder, and GM's fix over 30,000 miles is a new converter and filter.

What transmission fluid does a Silverado 2500HD 6L90 take, and how much?

DEXRON VI. GM's capacity table lists the 6L90, RPO MYD, at 5.7 liters or 6.0 quarts for a pan and filter service. That is not a dry fill, so set the final level at the check plug with the fluid in the service temperature window.

Does the Silverado 2500HD diesel use the 6L90?

No. GM's 2016 Silverado HD specification sheet pairs the 6L90 with the Vortec 6.0L gas engine and the Allison 1000 with the Duramax 6.6L diesel. Check the RPO label for MYD before using any 6L90 information.