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Thread: 2018 GMC Sierra / 8 speed issues/questions

  1. #1

    2018 GMC Sierra / 8 speed issues/questions

    Have been fighting a shudder with this truck, it has 15k miles on it & has been in the shop a few times for it (still under warranty). What I feel, almost feels like a miss fire, but no check engine light. When driving at constant speed, occasionally I will feel something, like a random miss fire, and when slightly accelerating I feel it alot, 10-12 times a second. Trans fluid was changed, nothing, changed torque converter, nothing, had it in last week for oil change & they changed the trans fluid again, said there was a new fluid out. For about 200 miles it felt different/better, it shifted when I felt it should, & didnt notice the shuddering. Now today on my way to work, it felt like it was back to the way it was before the last fluid change. Somewhere I read this transmission is a "learning transmission". Maybe they reset something while it was in the shop & now has "learned" how I drive & is trying to adjust for it....????

    So my question, is it possible that this is something electronic/PCM causing the shuddering? If so, can this be turned off so it doesnt "learn" from me....?

    Thanks,
    Scot

  2. #2
    Tuner in Training
    Join Date
    Feb 2019
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    10
    I don't have an answer but my 2016 / 8 speed is doing the same thing. It is in the shop now for a flush and fill. It tripped code PO711 - fluid low, dirty, or sensor and code PO700 - shift solenoid or faulty control module.

  3. #3
    Potential Tuner
    Join Date
    Sep 2016
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    Michigan
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    If you have a shudder, it's due to a bad torque converter. There is a service bulletin out for it. If you push GM they will pay for most of it even past 100,000 miles. I had to have mine replaced.

  4. #4
    Tuner in Training
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    Feb 2019
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    My dealer just called and they did the SB- replace with some new Mobile 1 fluid and replaced the harness and re-flash. I haven't picked it up yet but will report back. They said they did not need to replace the converter....we'll see.

  5. #5
    Tuner in Training
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    Quote Originally Posted by ragtopz28 View Post
    My dealer just called and they did the SB- replace with some new Mobile 1 fluid and replaced the harness and re-flash. I haven't picked it up yet but will report back. They said they did not need to replace the converter....we'll see.
    Picked her up and so far shifts better than ever. Smooth, no surging or hard down shifts. Fingers crossed.

  6. #6
    Quote Originally Posted by V3locity View Post
    If you have a shudder, it's due to a bad torque converter. There is a service bulletin out for it. If you push GM they will pay for most of it even past 100,000 miles. I had to have mine replaced.
    I have had it flushed, new fluid, they reported it didnt fix it, so they replaced the torque converter (less than 10k miles), & was in a couple weeks ago with flush & filled with new formula fluid. Still exists.

  7. #7
    Quote Originally Posted by ragtopz28 View Post
    Picked her up and so far shifts better than ever. Smooth, no surging or hard down shifts. Fingers crossed.

    After last fluid change, it was good for about 200 miles, then back to way it was before, maybe a little worse. What harness they change?