Shifting Issues

[tahjoe]

2019 Tahoe LT 4x4 with 65k miles. If I’m coasting at 40mph+, lift my foot off the gas pedal, and then lightly accelerate, the rpm gauge slips several hundred RPMs (even though I’m giving the car more gas) before catching. Makes merging on the highway a pain. This issue is repeatable at various speeds. But it also disappears (or seems to) when I’m in manual. Transmission usually runs around 190.

Took it to a dealership tech who said car is just “searching for the right gear,” but that I shouldn’t really feel the shift. They said that the transmission looks good, that 190 is a normal running temp, and that it was likely just a programming issue. He said it may be worth reprogramming the TC to disable [whatever it’s currently doing] in gears 1-4.

No codes / have never flushed the transmission.

I’m assuming the issue is my TC. I’m also assuming my transmission is chock-full of metal shavings and will fail sooner rather than later.

If I replace the TC and my transmission subsequently fails, would I be able to re-use the aftermarket TC? Or does the TC get fried whenever the transmission fails?

Goal is to delay the inevitable as long as possible, but I also don’t want to end up buying a new TC twice.

Appreciate y’all’s thoughts

 

[Marky Dissod]

Regardless of whatever GM says, ATF should be changed every 30k.
You may want to very seriously consider having your old ATF analyzed,
it may give you better more specific answers than blind guesses based on some typed words.

Do you 'really feel' the shift? Or do you just notice the 8L90 (or 10L80?) taking too long to make up its mind?

GM OE torque converter clutch programming engages / disengages it GRADUALLY, so it isn't felt as a distinct BUMP.
This reduction in NVH sacrifices the TCC's longevity and durability.

When you use manual shifting, the tcm most likely commands more line pressure, which MASKS the problem.
Eventually, this won't work either, too much wear will accumulate, and you may need a tow truck.

Once the TCC is worn out enough for a normal person to notice the slip,
the transmission is usually living on borrowed time, which is why I mentioned old ATF analysis.
Once the gear clutches are worn out enough for a normal person to notice the slip,
it is almost over.