I have an 02 GMC sierra that shifts funny.

[roosternugget]

I have an 02 GMC sierra 5.3. It's got a transtar 4L60E kit, with a custom torque converter (24-2800 stall). It's also got a rear main leak, and a leak from the transmission-transfer case gasket (adding in case its relevant, stays constantly topped off). My transmission shifts funny at operating temp (no transmission temp guage) when it's cold it shifts like it's supposed to, but once it's hot, it'll Rev to 4K RPM, slam into third, then sometimes back to second. Other times it'll hik 4K RPM, then hit 2nd for a split second, then third. I think its overheating, but I was also told it could be the TCM. I have an 11 hour roadtrip in a few days (fixing leaks before then). Just trying to figure out what I need to fix when I arrive at my destination, I also have a mishimoto trans cooler "getting ready to ship".

 

I forgot to add: it's only on the 1-2 shift from acceleration. Once it's in 3-4th gear, it shifts like normal. I also have no codes with about 3K miles on the transmission. Shop says it was a full transtar rebuilt with new valve body and all new solenoids

Edited October 3 by roosternugget
Forgot to add