These three come through the door regularly, and they each have a predictable misdiagnosis attached. Knowing the pattern saves you the R&R on a unit that didn't need to come out. 1. "Harsh 1-2 shift, especially when cold" — misdiagnosed as TCC apply issue. On the 6L80E, a harsh cold 1-2 shift with no slip is almost always PC-A solenoid response time. The valve body bore for PC-A wears oval over time; the spool doesn't seat cleanly and pressure overshoots during the upshift. Shops chase the TCC because the customer describes a "thump," but TCC doesn't engage until 3rd gear at light throttle. Pull live data first. If adaptive shift pressure is maxed out and PC-A duty cycle is hunting above 60% at idle, the bore is worn. The solenoid alone won't fix it — you need the Sonnax sleeve kit for the bore.
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