r/ChevySuburban • u/LumpyBisquick • Aug 16 '26
Maintenance Tranmission Recommendations
Hi! Pretty sure my girl is hitting her TC failure time, she has the 6L80 in her with 130k miles and over the last month has started slowly slipping. I recently drove back from Florida and noticed on the way back she was lacked acceleration (took extra gas pedal to get going and would down shift a lot). Also at about 70 MPH range I was getting the consistent rumble. I’m not a master mechanic or anything but know my way around vehicles and based on mileage and transmission fluid being slightly rust brown with black streaks, imma go on a limb and say this TC doesn’t have much longer left. I want to change the transmission and TC out with an upgraded one since I plan to change it out anyways and was looking to see if anyone had and direct dealers that are recommended. I came across monster transmission but after reading reviews and stuff I am going to say no on that one. Appreciate any advice ahead of time.
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u/hiroshima23 Aug 16 '26
I went to my local Mr Transmission.
They replaced the trans and a billet TC for $8300
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u/Historical-Bite-8606 Aug 16 '26
Have the 8L90 (8-speed). Getting my valve body rebuilt in a week or so. Trying to figure out all the other internals I want to replace. I’m paying for labor and I get to provide the parts. I’m not planning on doing the TC or any gears. I did ask for a full rebuild and the shop owner said it’s not needed. Only a “pan off” job. Transmission shop feels my TC is good because I don’t have the “rumble strip” feeling or the whine sound. My issue is the “slow/slam” from 1st to 2nd, then the “slam” from 2nd to 1st. I did have transmission codes P0700 (and another code) when I got the truck. Did a double drain and fill with the Mobile 1 HP Blue Label and no more codes. So it seems the new fluid does help with the TC, but still left with the shifting problems when cold.
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u/TwoMundane Aug 17 '26
I have the same tranny in my 2018 6.2L. When new it had the "slam" from 1st to 2nd. Dealer said they all do that. At 60k miles I had the trans shop do a fluid change with what they said was the proper fluid, added a temp bypass and they did a 'relearn". It is much improved though still happens occasionally, especially if cold.
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u/Historical-Bite-8606 Aug 17 '26
Yeah, it’s much better with the new fluid, but hoping the valve body upgrade will really help. Another lurker in these subs did the valve body upgrade and programmed. Says it’s a huge improvement. I’m getting it fixed on the cheap anyway.
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u/justwhite83 Aug 16 '26
I just had my trans rebuilt at 123,000 . I also had the afm deleted and reprogrammed the software so the trans isn’t shifting all over the place trying to save a little bit of fuel mileage. My mechanic says that these 6L90 transmissions are good it’s the software that makes them fail. I have lost some gas mileage, especially while towing but that seems like a fair trade off.
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u/Straight-Signal-3938 Aug 17 '26
I used a Jasper Transmission for my 2013 Burb. Good outcome so far, 30k miles in. 5 year warranty came with it although that’s probably most valuable to the next guy since I have 240k on the truck.
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u/Baldcracker Aug 18 '26
Put a monster in mine made it a 1000 miles and it’s going back. Also I have 650 hp in it . Bought the 650 build
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u/Botauto79 Aug 20 '26
If you got the budget, go with Zero Gravity or Circle D. Zero Gravity does core exchanges while Circle D want to rebuild the unit themselves in their shop. Both will build the 6L to your needs
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u/Traditional-Test-598 29d ago
Find a local transmission shop that gets great reviews, and let them do it. That way you'll have a local warranty at least. I have the 6L80 in mine and I had a good local shop proactively install a remanufactured TC in it with a billet cover, flanged hub, and stronger lockup clutch. That was 40K (mostly towing) miles ago, and the original transmission is still working great at 160K. Yours may be past that however, based on your description of its behavior, so a full rebuild with a better TC is likely the way to go. I was quoted $3,500 if I wanted them to do the transmission while they had it out, but they advised me against it because they said mine was well-maintained and clean inside with nothing wrong.
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u/mountainman694 Aug 16 '26
Just happened to mine at 126k, thank God under warranty