2015 GMC Yukon 8L90 Lurching Shifts

dwchapmanjr · December 2, 2019

I have not seen a whole lot posted on this and tried to search first. Recently I started noticing a rough shift pattern. I can't tell if its 2-3, 3-4 or 3-4,4-5. It is under light acceleration and been a bit colder. It seems to lurch when making those two shifts. I need to do some driving to test further to see if it progresses through the rest of the shifts or clears up after warmed up.

Curious if anyone else has run into this and if there are any troubleshooting steps I can do without any special tools/scanners. I am due for a scheduled visit to the dealer and will have them look into it but found the more information I can provide them the better. Still under powertrain warranty (5 year/100k)

I don't have the TCC shudder anymore after the latest fluid change about a year ago but I have gone through a few fluid changes and a TCC replacement.

I have read where if this clears up when its not cold that may be expected. I'm wondering if I have a solenoid starting to freeze. Probably not a lot I can do without a scan tool that can read from TCM but thought I'd ask.

Havasubum · December 2, 2019

My 8 speed transmission acts up whether it's hot or cold. Basically the shift patter between 1 and 2 is defective. At low speed and feathering the throttle (e.g looking for a parking spot) the trans will suddenly upshift into 2nd. propelling the truck faster. My fear is that it could cause an accident. It will do the same thing when "tipping" the throttle after slowing and gradually increasing speed. The trans will violently downshift into first, throwing my head into the headrest. GM has replaced the trans fluid with synthetic and replaced the valve body. Nothing has worked so far. It seems to be getting worse with age. I have 32k miles on the truck.

dwchapmanjr · December 2, 2019

3 minutes ago, Havasubum said:

My 8 speed transmission acts up whether it's hot or cold. Basically the shift patter between 1 and 2 is defective. At low speed and feathering the throttle (e.g looking for a parking spot) the trans will suddenly upshift into 2nd. propelling the truck faster. My fear is that it could cause an accident. It will do the same thing when "tipping" the throttle after slowing and gradually increasing speed. The trans will violently downshift into first, throwing my head into the headrest. GM has replaced the trans fluid with synthetic and replaced the valve body. Nothing has worked so far. It seems to be getting worse with age. I have 32k miles on the truck.

Interesting that valve body replacement did not fix this one. My issue is definitely different than this but thanks for sharing. I hope you find a resolution. I dealt with the TCC issue for a while before anyone really knew how to fix it so I know how frustrating these types of issues can be.

dwchapmanjr · December 2, 2019

I did come across 16-NA-213 which while it doesn't apply to my transmission manufacture date did lead me on a trail to go to

14-07-30-001 - Which pointed me to 16-NA-411 as 14-07-30-001 is Corvette specific. 16-NA-411 is truck specific and points to a new dealer calibration (which I believe I have had done) and lets me use 16-NA-019 to train the shift adapts.

Seems somewhat painful but it may just work as I noticed the issue became harder to reproduce the more I tried.