Hunter_alexander

Just wanted to give an update. Problem is solved. Spoke with the service manager who was extremely helpful and knowledgeable. Apparently the Canadian built transmission (8spd) when they were first building them, they used too much assembly lube, causing the clutch packs to "shudder" as they slipped. That is also why the rpms go up, as the trans is basically slipping. The TSB noted above flushing the trans 3 times, reprogramming and relearning the shifting, solves the issue as it gets the lube flushed out and the trans fluid can soak back into the clutch packs as it should so they can engage and the friction is there as it should be. Allen, the service manager was great to work with and said my initial diagnoses was spot on and was thankful I was as "in tune" with my vehicle as I was. It helped him a lot. Truck drives nice and smooth, like silk now. Very happy and glad I found this place to assist in the diagnoses. Thanks all!!

Thanks for the help. Ive done some more diagnosing. When it shudders like that, and the rpm goes up its that the clutch pack is slipping in gear. Light acceleration, the shudder, rpm goes up at the same time and then rpm goes down when the shuddering stops.

Good morning everyone. New here. Names Craig. Sorry this is a bit long winded but here goes... I just purchased a 2016 GMC Sierra SLT with 38k miles on it from Dave Hallmans Chevy in Erie Pa last Monday. Very happy with it and the purchase process. Unfortunately, even with test driving it, after less than a week of driving it, started noticing vibration issues. It wasn't all the time, and it would and wouldn't happen on the same stretch of roads. So definitely intermittent. Here is what I did find after reading the threads on here and other forums and internet. Steady stretch of road, between 25-55 mph, throttle steady, not accelerating, not decelerating, if I watched the tach, it would jump up and then go back down by a hundred or so rpms. When its doing that, there is a shudder, vibration in the steering etc. I believe my issue is in the transmission, and more than likely the torque converter locking/unlocking and not sending/creating constant pressure for the trans, causing slipping. Now, that being said, I have read It mentioned the TSB https://static.nhtsa.gov/odi/tsbs/2019/MC-10154635-9999.pdf and I believe that might be my issue. There was discussion of the torque converter being replaced, and other where they flush the trans 3 times, then reprogram the computer and drive so the trans can relearn how to shift. Ive been working on cars since 16 (Im 47 now) and have restored cars from the ground up, built engines trans, electrical. I have learned to do it all. Im looking to take the truck into Hallmans for service, but looking for advice on how to approach it with the service manager. Can I get a service tech to ride along with me so I can show them whats going on? Ive always purchased used, but always did the work myself as they were cheaper trucks and cars with no warranty. Now Im in the position of having a really nice truck, but not used to dealing with service centers to get repairs done. Thoughts on approach and diagnosis?