6L80 woes.... But haven't got all the symptoms.....

[Kapitein]

07 Denali XL. 175k miles.

Last gearbox oil change 12m/10k miles ago.

Fluid is pink and looks/smells good and is filled to correct level.

Problem:

Every now and again (but not always) it will surge a little under low and medium throttle and when the fluid is warm. Can be low speed or highway speeds. You can feel it and see it on the tacho... However it's not the 2-300 rev variation a lot of people describe. It's more like a 100rpm variation.

It's getting slowly more common/worse IMO.

It does not shudder at all. So obviously some of the symptoms fit a bad torque converter, but the lack of shudder has me doubting a little.



MAF is new. Could a small vacuum leak on the intake side cause similar problems? The car also sometimes has a minor rev variation at idle (in P)......

Thanks for any insights and sharing of experiences....

 

[B-train]

Does the surging only happen in 6th gear with torque converter locked up? Have you tried driving in 5th to go the same mph and how does it act? What is the Trans temp when acting up, if repeatable.

I would suspect a torque converter where the TCC is allowing too much slip. Most new vehicles have gone to a viscous type of lockup that allows for rpm variation even when "locked up." Not like the old school days of the 90's when lock-up meant direct drive.

One last thing. What fluid did you put in at the last service? Dextron 6?