2018 Tahoe 5.3L 104,000 mi oscillating. RPMs and shuddering when low RPMs and under load/ accelerating

[slackert9x]

Transmission service performed about 5,000 mi ago (problem had started just before this but has gotten worse since). At low RPMs and accelerating the car shutters. The RPMs also randomly oscillate, seemingly randomly ( especially cruising between 35 and about 50 mph). Transmission fluid level is seemingly fine (checked at approximately 170° on flat ground, shifting slowly through gears and back into Park, let idle for about 1 minute). No codes on dash. There is a intermittent misfire on cylinder. 5. That has been going on for a few months as well. At 100,000 mi oil change was done, spark plugs replaced, spark plug wires, Air filter, throttle body cleaned and MAF cleaned. Swapped coils between number five and number three but intermittent misfire still remained. I have an x-tool d7s scanner, so I can see the intermittent misfires.
My car knowledge is about average. It can do most basic maintenance and repairs. My guess is I'm having some problem with the torque converter and as far as the cylinder 5 issue, my next guess is the fuel injector.
Any help would be great, thank you in advance

 

[TheBigCheezeBall]

From what little I know, and it’s not much, the shudder combined with the RPMs jumping around, seems like the torque converter clutch. Not sure with the #5 missfire, but i would try to swap that plug and see if it helps.

 

[slackert9x]

That's my first thought as well.
I already swapped in new plugs with no change. I did pull the plug last week and overall it seemed fine though I didn't notice a little bit of oil that had made its way up to the upper part of the threads.

 

[ReaperHWK]

You still can’t rule out a misfire and you have a code for it that is still there. That means you need to fix that before throwing money into the trans IMO.

I had a misfire in my 2015 that didn’t go away with plugs/coil change and it was a fuel injector. I’d do that if I were you. When you change out the injector since the whole rail on that side needs to come out I did all 4 on that rail. To me it was worth it so I don’t have to pull that rail out again for another injector that is the same age as the failed one.

Also if you have a descent scanner you can display the live misfire counts. I’d do that and drive the truck and see if the truck shutters or misses when the misfires are actively occurring.

For the torque converter you can monitor the slip speed and tell if that’s going as well. I did that recently and posted about it to diagnose a bad converter. Search my profile for threads created.

All this troubleshooting and failures on mine I traded it in for a 2026 now I have no problems except the payment! lol. Was taking way too long much time to fix all this crap that was failing on my 2015 LTZ with 170k miles.

 

[LSCALADE]

2 Paths at this point.

Path 1 is new TC perhaps get a 6L90 unit, fluid flush and new filter and proceed.

Path 2 if you dont want to do the TC swap is to get HP tuners or someone with access and make some adjustments.

At the current worn-out level of the clutch material, the cluch is designed to slip but also hold a certain amount of torque and you are exceeding that torque with the factory settings.
A couple of things to be done are:
Zero out the slip tables.
Increase offset pressure from 26.6psi, which is your stock setting to something higher try 50psi.
Increase gain from lets say 0.375 to say 0.5.
Slip error tables you can increase the numbers to the right of the 0rpm slip. 30% as a start.
Change the lock up speeds, remove lock-up from 1-4. and lock up in 5 and 6 only.
Log the vehicle and note at what level load you start to see fluctuations. Then, you can go in and release the TCC above those loads, which will help the clutch prolong its life.

I am going on a full year of driving with a bad TCC and all these changes have helped it last without further degradation. TCC shudder does not even happen any more because I let the TC clutch loose above the torque levels where it cant hold.