2015 Yukon 6L80 transmission suggestions?

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DerekRinger

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Hello! New member and first time poster. Looking for some guidance on our 2015 GMC Yukon SLT. It's the 5.3 with the 6L80 transmission. About 110,000 miles on it.

So just over a year ago we started experiencing the dreaded shudder around 1500-2000 rpm. For a long while I just assumed it was a mis-fire or bad injectors or something. Did quite a bit of maintenance and never figured it out until recently when I discovered these forums, and apparently it's a very common problem with theses transmissions. The final straw that solidified that it was in fact the transmission, or just the TC, occured about a month ago when my family went on Vacation. We drove a couple hundred miles on the freeway, still experiencing the shudder, but otherwise driving fine. We let the car sit a few days then went to drive it and the transmission wouldn't engage when I put it drive. After shutting it off and letting it sit for a few minutes, I was able to drive it for a mile or so before it would seem to slip or disengage again. Then just repeat the process of shutting it off, letting it sit, then restarting it to get us back. I put about 4 miles on it doing this method to get us back to where we were staying.

Anyways, we had it towed (trailered) those 200 miles back home. After doing some deep diving on the internet and watching quite a bit of YouTube videos, I decided to pull the pan and change the filter and fluid. There was a decent amount of a metallic paste like, burnt fluid in the bottom of the pan and around the magnet(I'll try to attach a short video). But, after doing so, the car was able to drive again almost like normal, with almost no issues. It still slightly had to shudder, but almost barely noticeable. I drove it around for about 50 miles then it started to act up a bit; shuddering, slipping a bit, and frequent and harder shifts. I brought it home, checked the transmission fluid, and I was about half a qt low, so I topped it off. Since then, it has been driving great! And the shudder is virtually gone (barely noticeable up really steep hills, when I'm almost trying to make it do it by babying the accelerator).

So anyways I guess my question is; do I still take it into the transmission shop for a rebuild when the problem seems to be gone now after the fluid and filter change? It's scheduled to be dropped off next week the day after Christmas. But, if there's a chance I fixed the problem, we sure could benefit from not spending the $6k we were quoted to rebuild it. The tech said they obviously will fully diagnos and inspect it before the deem a rebuild. Or was my fluid change just a temporary bandage and the transmission will inevitably fail? We though about just getting rid of the car, or trading it in, but we still owe $12k on it and we do like the rig quite a bit, minus this issue.

Just looking for some insite and guidance from some people more experienced and knowledgeable than myself. Thank you!
 

Marky Dissod

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Either your TCC or your transmission is on borrowed time.
Really cannot hurt to change the ATF again.
Have you disabled Engine Half@$$? V4mode is what prematurely ages the TCC.
When the TCC fails, it barfs into the ATF, which schidts the transmission immediately after.
 
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DerekRinger

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No, I have not disabled the V4 mode. I honestly didn't realize that you could, but I originally thought that's what was causing the shuddering because it seemed to be shuddering when I would watch the display showing it go from V4 back to V8 at slight acceleration. I'll have to dig into these threads to see how to do that.

I kind of figured I was on borrowed time, so I'll still drop it off at the transmission shop to avoid having my family get unexpectedly stranded at some point. I just needed some more people to confirm that, cuz dropping $6k right after Christmas is painful.

Thank you!
 

Marky Dissod

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... have not disabled V4 mode.
I honestly didn't realize that you could, but I originally thought that's what was causing the shuddering because it seemed to be shuddering when I would watch the display showing it go from V4 back to V8 at slight acceleration.
I'll have to dig into these threads to see how to do that.
Short answer: get ecm tuned.
No one ever regrets this (unless they're on the wrong side of the Dunning-Kreuger event horizon).
Longer answer:
Tuner typically
lifts minimum engine coolant temp to enable Engine Half@$$ over 248F?
lifts minimum engine run time to enable V4mode over 6hrs?
lifts minimum road speed to enable V4mode over 135MpH?
drops maximum engine speed to enable V4mode under engine's minimum possible idleRpM, 250RpM?
drops maximum TPS% to enable V4mode to 0.0% throttle
And that's how you or anyone else disables Engine Half@$$.

(If for whatever strange reason, you're interested in using V4 mode as an overheat mitigation mode,
I can show how to do that too.)
 

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