Transmission Issues

[bwhite]

I have a 2017 Tahoe LS 5.3LV8 with 51K miles. Bought in October 2021 with 40.8K miles. I am dealing with a couple issues:
1. Sometimes when coming to a stop, transmission feels like it's down shifting in first gear like a manual.

2. I notice at highway speed when using cruise control or not, it hesitates when accelerating. Fuel filter or throttle body issues maybe?

3. My gas petal seems real touchy. I know cars today use sensors and not cables to old days.

Prior to this vehicle, I drove a 2007 Tahoe LS 4.8LV8. Great truck. With 10 year difference in technology, I'm wondering if
I am just not used to the behaviors on an updated model of if something else is going on. I have no check engine lights, or any other indicators that anything is not working properly. My grew up with cars from the 60s and 70s where you learned about problems based on how something felt, sounded or smelled. Any feedback would be appreciated.

 

[blackelky]

I think it's the gas saving technology and afm where the cylinders shut off

 

[Marky Dissod]

... 2017 Tahoe LS 5.3LV8 with 51K miles ... dealing with a couple issues:
1. Sometimes when coming to a stop, transmission feels like it's down shifting in first gear like a manual.

If you were more specific about the speed window through which you were decelerating - say, from 13MpH to 4MpH, for example - a tuner who knows GM's OE shift tables would tell you if it was downshifting from 3rd to 2nd or 2nd to 1st at that moment.
Otherwise it's just guesswork.

2. I notice at highway speed when using cruise control or not, it hesitates when accelerating. Fuel filter or throttle body issues maybe?

3. My gas petal seems real touchy. I know cars today use sensors and not cables to old days.

'At highway speed' in NYC can be anything over 25MpH, which is close to the cruise control's lower operational limit ...
Again, more specificity would be helpful. That said, this time, I'll take a guess.

I've a 4L60E, and a physical throttle cable. If I step on it gently enough to avoid downshifts to 3rd or 2nd, the TCC unlocks, and I'll get a pretty quick response, because the throttle moves as quickly as my foot.
If I step harder to downshift to 3rd or 2nd (my pcm is tuned for quicker throttle AND transmission response), again, I don't wait long.

Don't know if you have an 8L90 or 10L90, but between your foot and the throttle are a few things which edit how quickly the throttle moves in response to your foot (never quite as quickly, sometimes much slower), as well as a transmission that prioritizes efficiency (MpGs) over driver satisfaction under 75% throttle.

GM has probably slurred the throttle response to give the transmission more time to decide whether to downshift to 7th or 6th or 5th or 4th or maybe even 3rd. They also don't really want you to kinaesthetically notice the precise moment the next gear engages, because GM thinks most drivers don't want to risk upsetting their latte with the sensation of up- or downshifts.

Prior to this vehicle, I drove a 2007 Tahoe LS 4.8L V8. Great truck.
With 10 year difference in technology, I'm wondering if I am just not used to the behaviors on an updated model of if something else is going on.
I have no check engine lights, or any other indicators that anything is not working properly. I grew up with cars from the 60s and 70s where you learned about problems based on how something felt, sounded or smelled. Any feedback would be appreciated.

For whatever it's worth to you, I grew up in the 90s on LT1 Caprices, each of which was tuned to enhance feedback at all times.
This runs directly counter to GM's philosophy of not letting you feel anything until it becomes potentially expensive, at which point the only cryptic feedback you get is a 'Check Engine' light that you have to hook up a device to just to decipher the code(s), which may be the actual problem, close to the actual problem, or merely a symptom of the problem; no way to know til you check the code(s).

If GM's definition of 'properly' differs from yours - it likely does - then have your ecm & tcm tuned.

 

[sealandsky]

Regarding your transmission - It sounds like you have the 8 speed and for that transmission, clunky downshifts are pretty much normal. Actually clunky behavior regularly or randomly is pretty much normal. You can check with your dealer for any service bulletins that may not have been accomplished and also have them do the fluid flush and update, but otherwise your only fix is to buy a newer rig with the 10 speed (which is a very good transmission).

 

[alpha_omega]

What upgrades/updates have you done to the tranny since purchasing it?

 

[Marky Dissod]

From wikipedia:
"The 8L90 is the subject of a class-action lawsuit filed in December 2018 that alleges the transmission suffers from persistent "shudder" issues, that GM has known about the problems since its introduction, and has failed to provide a solution, instead choosing to wait until the unit is out of warranty."

The following article

ATI Performance Is Beefing Up GM’s 8L90-E Eight-Speed Transmission

GM’s 8L90-E transmission is becoming a favorite automatic transmission with performance enthusiasts. ATI Performance offers room for improvement.

www.chevyhardcore.com

contains this morsel of info which is likely relevant to your complaint:
"Many vehicle owners with the stock 8L90E have reported an inherent “shudder” issue and harsh shifting problems with the transmission.
GM issued Technical Service Bulletin 18-NA-355, with updates that address the “torque converter clutch (TCC) shudder conditions.”

The problem was identified by many customers who reported ... shuddering frequently and shifting harshly between 1st and 2nd.
The same harsh shifting was identified when shifting down between second and first gear.
The issue was magnified when accelerating during the upshift or decelerating in the downshift.

GM identified a fluid flush as a probable fix for the issue ...
According to GM, the issue was caused by “moisture content in the transmission fluid.”
The old GM transmission fluid was to be swapped out for
Mobil 1’s new synthetic LV ATF HP fluid
which seems to have solved many of the issues."

I personally prefer any of these:

Automatic Transmission Fluid Protectant - Lubegard

www.lubegard.com

PLATINUM ATF Protectant - Lubegard

www.lubegard.com

COMPLETE Full Synthetic ATF - Lubegard

www.lubegard.com

 

[K2 Kaiju]

The 17 LS 5.3 has the 6 speed. Tune out AFM and firm up shifts with a Diablosport or custom tune. Change out fluids as well...

 

[NickTransmissions]

I have a 2017 Tahoe LS 5.3LV8 with 51K miles. Bought in October 2021 with 40.8K miles. I am dealing with a couple issues:
1. Sometimes when coming to a stop, transmission feels like it's down shifting in first gear like a manual.

2. I notice at highway speed when using cruise control or not, it hesitates when accelerating. Fuel filter or throttle body issues maybe?

3. My gas petal seems real touchy. I know cars today use sensors and not cables to old days.

Prior to this vehicle, I drove a 2007 Tahoe LS 4.8LV8. Great truck. With 10 year difference in technology, I'm wondering if
I am just not used to the behaviors on an updated model of if something else is going on. I have no check engine lights, or any other indicators that anything is not working properly. My grew up with cars from the 60s and 70s where you learned about problems based on how something felt, sounded or smelled. Any feedback would be appreciated.

Figure out your hesitation at higher speeds first as they may or may not account your symptoms w/the trans.

Clunky up/downshifting in 6Ls is often minor cross leaks in one more locations in the compensator feed (CF) hydraulic circuitry. The CF is responsible for accumulation, mechanical shift timing, apply/release of clutch packs and centrifugal apply prevention inside the case but if seals, sealing rings or other parts of that circuit wear, the mechanical timing of apply and release of the different sets of clutches coming on and off as gear changes are commanded starts to deviate from spec and timing is off...the end result is jerky, clunky shifts at first and as wear progresses, flaring, partial tie ups and clutch failure result. I wouldnt expect to see this at only 40k-ish miles though...

Put a bi directional scan tool, drive it and look engine, fuel system and other related live data streams as well as trans data to see if anything pops out at you.