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2020 GMC Sierra 2500HD Denali 6.6L Gas


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My truck with 40,000 miles on it would shift real hard , with a bad clunk , mainly when I was coming to a stop , and then as I would accelerate . Took it to my local dealership . They ended up changing the valve body . It now has 45,000 mile on it , and is starting to do it again . Going to the dealership again this morning . 

It's just frustrating , when you pay this kind of money for a truck , and it has these issues . I hate to say it , but I have owned Toyota's before , with never an issue .

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2 hours ago, Wade Palmer said:

My truck with 40,000 miles on it would shift real hard , with a bad clunk , mainly when I was coming to a stop , and then as I would accelerate . Took it to my local dealership . They ended up changing the valve body . It now has 45,000 mile on it , and is starting to do it again . Going to the dealership again this morning . 

It's just frustrating , when you pay this kind of money for a truck , and it has these issues . I hate to say it , but I have owned Toyota's before , with never an issue .

Do you tow heavy? Same trailer with Toyota? All makes can have issues. 

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GM HDs going back to the 6.0s do this. I am convinced it's in the tuning. It should not dump into numerically high 1st gear unloaded until at rest or commanded throttle is >30% in my opinion. It should act like it currently does only in Tow/Haul. Likely, some jackass wrecked it towing out of tow/haul mode and sued GM so they force a geared deceleration shift plan into the tune instead of acting like any other automatic transmission vehicle since 1996 (doing what I said in third sentence).

 

It will not be a mechanical fix. Sounds like they threw parts at it the first time. If you are truly tired of it enough to spend money, find someone that knows HP Tuners and spend the coin to get into the tune. That's where you'll find solace.

Edited by Epsilon Plus
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Good afternoon . Thanks guys for listening . My truck is at the dealership right now , has been there since last Thursday .

They are changing out the valve body again , and apparently last time they did not change out the TCM . So this time they are changing both . Keeping my fingers crossed ! They did the transmission drain the first time this happened , along with changing the valve body . Front and rear diff's were changed about a month ago .

So you think it could be all in the tuning ? How much does something like that usually cost ? I have never towed or hauled anything , and had the dealership , check to make sure it wasn't stuck in tow/haul , and maybe just not showing up on instrument panel . I live in Michigan , would you maybe know of a good tuner ? 

Thanks 

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