2013 Silverado 6L80E shift problem

[Butter2]

The 6L80E transmission in my 2013 Silverado 1500 recently overheated and started slipping. While rebuilding the transmission I found the plastic alignment plate had melted in the oil pump. I replaced all the clutches and seals, the oil pump, bell housing and reinstalled the transmission back in the pickup. When I took the pickup out for a test drive it would shift 1st and reverse normally but when I would accelerate to where it should shift into 2nd it acts like it's slipping and then all of a sudden grabs and almost stops the vehicle and goes back in the first gear. I believe it's locking into limp mode. I hauled the pick up to the dealer and have them reprogram the transmission but that did not fix the problem. It's not throwing any codes so I'm not sure where to look next. I'm wondering if the TCC/shift control solenoid got too hot and is no longer shifting.

 

UPDATE: I haven't done anything new to the transmission other than let it sit while I discussed different options, but when I went to move the pickup it drove forward 50 ft and locked up. I can back up but it will not drive forward. The only thing different is the outside temperature has cooled off since I test drove it 2 weeks ago.

Edited September 24, 2021 by Butter2
Update on symptoms

[Jsdirt]

Something went wrong on the rebuild, sounds like. That doesn't sound at all like limp mode to me. Sounds like it's trying to go into 2 gears at the same time. Something was not assembled correctly. I would get on a scan tool and look at every transmission parameter in live data. Make sure things are doing what they're supposed to do ... and if they're not, you've got a problem internally.

 

There's 2 things I'll never do on modern automobiles - body work, and transmission rebuilds. With rebuilds, there's just FAR too much that can go wrong, and it's A LOT of work to correct if it does. ONE little seal mixed up with another that looks nearly identical will cause all kinds of issues. A check ball missing or in the wrong spot will do the same, as will a bearing or bushing seated too deep, or not deep enough in its bore. I couldn't do enough of them in a year to remain proficient. That's why there are guys who do nothing but this type of work. It's friggin HUGELY time consuming, and these days, a pile of back breaking work (Even more so if you live in the salt belt). No harm in trying - I've figured alot of things out over the past 35 years of playing with automobiles and motorcycles, but I've also learned to pick and chose my battles these days. This is exactly why I'll never go deeper than a filter swap on a modern automatic.

 

You've got 2 options, and none of them are good. One is going to cost you a mountain of cash, and the other is going to cost you a weekend of labor. Either yank the trans, go through EVERY single part you touched over again, or yank it and bring it to someone who does several of these a week.

 

I recently had a transmission failure of my 4L60E. I contemplated diving in and replacing the 3 / 4 clutch pack ... but boy am I glad I decided against that route! Would've been a temporary bandaid on a modern trans with 103k miles on it. It took me 2 friggin weeks to get that damn transmission out, and get the new one in! WITH A LIFT! Every single part of the job fought me from start to finish. Biggest nightmare job I've EVER done in my life, thanks to GM engineering and it's love of low-bidder junk metals and parts.

 

I bought a brand new Heavy Hauler transmission from PerformaBuilt in PA, built precisely for how I use my truck - best decision I've ever made. It's changed the entire performance characteristics of the truck. Feels like it gained deep double-digits in foot-pounds of torque, and shifts fast and firm in ALL gears, even lockup. I absolutely love it. Best transmission I have ever owned, hands down. Works like a friggin dream! It wasn't cheap in the slightest way, however. You get what you pay for (As long as GM didn't build it!!).