2017 Denali Shifts hard into first gear

[Havasubum]

I did a quick search and couldn't find anyone with my problem.  The 8 speed trans in my 2017 Denali is increasingly shifting hard into first gear.  Occasionally it will shift hard while slowly coming to a stop at a signal during normal around town driving.  The other day I made a left turn slowly onto a street with an incline.  When I applied a light amount of power, it shifted so hard into first that my head hit the head rest.  When mentioning hard shifting to the dealer, they say that it is the nature of the beast.  I sold my 2011 Denali to my son.  I am really missing the 6 speed trans.  Has anyone else had this problem and found a fix?

 

Thanks everyone

 

Jerry

[blakearc]

Hi Jerry,

 

I recently purchased a pre owned 2017 GMC Sierra Denali with 30k miles. I am experiencing the same issues you are. For me its when I leave my house in the morning for work and pull up to my first stop sign in my neighborhood and get a very harsh down shift into 1st gear. It seems to be the worst when coming to stops at low speeds. The truck will lunge forward, its very annoying. I brought the truck to a local dealer who says they have identified the hard shift and applied a "relearn process". I was excited to think that this may fix the problem but it did not and my truck still has the same hard shifts/clunking. I am considering ordering a Range AFM disabler device as I've read that it improves shifting but I'm not 100% sure this will fix our problem (Maybe another member can chime in?) Do  you have any updates or fixes for this problem yet? 

[Havasubum]

Thank you for your reply.  I had the same procedure.  They flashed the ECM and erased the learning matrix.  I found it to be marginally better.  I personally would shy away from anything after market.  I wouldn't want GM to not cover the warranty.

 

Thanks

[blakearc]

I agree, I would definitely prefer the issue to be fixed by GM. After searching this forum, this seems like a common problem with the 8 speed transmission. I love the truck but the hard shifting really bugs me. 

[Tahoe02]

I thought the proper procedure was to do a re-program and a fluid change to an updated fluid and if that does not work then a torque converter change. There should be a bulletin on this procedure.

[5proms]

I'm having the same issue with our 2015i Escalade ESV.  Same tranny, 8L90E.  It has had all the Field Action Recall items accomplished related to 8L90E shudder and driveability problems.  But, it still hard shifts between 1st and 2nd under very light accelerator pedal push.  If I 'lean' into it, punch it or we are towing, it shifts just fine. 

 

For background reference here are the service bulletins from 2015 related to this transmission:

N150396 15396 HARSH SHIFTING WHEN STARTING IN LOW TEMPS -  Corrective action was Trans Control Wiring Harness Replacement
N150389 15389 TORQUE CONVERTER CLUTCH (TCC) SHUDDER  - Corrective action was Trans module reprogram

 

Then in 2018 the dealer performed 8480478 Flush and Drain fluids for Trans shake or shudder.

 

Don't know if GM applied all these updates to 2017 models, but there is obviously a history with this transmission.