2017 occasional Harsh shifting

Brewder

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We recently purchased a "new to us" 2017 Tahoe with 38k miles. It is in mint condition and we received a 1 year full CPO warranty when purchased. We were told the previous owner was a soccer mom who took immaculate care of the vehicle (no towing) but honestly, who ever really knows. We just returned from a 1,200+ mile road trip and during those two weeks I noticed some harsh downshifts (I believe it was 3rd to 2nd) and what seems to be occasional odd transmission shifts / hunting.

I'm taking it to the dealership to have the Thermal bypass Valve installed (Service Bulletin 21-NA-199) and to do a transmission fluid exchange / filter change. I'm hoping to have it all covered under the CPO warranty.

I'm curious if anyone has been in this similar situation before, and what happened? I'm also curious to know if the actual trans fluid is different than the factory fill from back in 2016 when it was built...?


//Brew
 

Plimbob

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Brew,

I have a 2017 with the 6 speed and has 93k on it. At 89k, the trans failed, symptoms were jumping into neutral at a stop and hard shifting especially between 2-3rd. I took it to a reputable trans shop in our location and they stated the TC was going bad and shedding metal. They told me they rebuild 4-5 of these a month because of that reason.

I had it redone with a Billet TC, Sonnax valves and an updated thermostat. However, it is back to shifting hard again so it's going back the trans shop tomorrow for their review. We'll see what becomes of this.

I have read that tuning the TCM helps resolve this. I currently have a Diablo Tune by Lewis Eaton but I do not think there was much tuning done to the TCM just the ECM.
 
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Brewder

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I appreciate you sharing.. Not sure though if I feel better, or worse! lol. I honestly would love to trade my 2017 for the "redesigned" 2021 model (i want the 7ish extra inches of cargo space behind the 3rd row). but I don't hear great things about THAT transmission either.
 
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Brewder

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For whatever it's worth... Today the dealer did a fluid flush (kept the original filter installed) and they installed the new TBV all under the CPO warranty. I'm happy. On the short drive home the trans fluid is already running 172 degrees.... prior to the TBV it was averaging in the upper 180's..

//Brew
 
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Brewder

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Pressed submit too quickly... i'll post an update in a few weeks if we notice any real difference at all.
 

Plimbob

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Brew,

Do you know if they filled with the different (or revised) ACdelco fluid that has been discussed in various threads which supposedly resolves the abrupt shift problem?
 
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Brewder

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Good question. The paperwork I received had this line item:

Installed K19293024 DEX6 QTY 6.
 

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