My 2015 Sierra trans fluid is burnt looking. 121,000 miles on trans. 75,000 on fluid. Tech said pan was pretty clean for how dark the fluid is. Changed filter and refilled w new fluid. It did shift a little better after.

Questions are: what caused the burnt fluid and what problems should I be looking for? Should I dona flush to replace all of the fluid or do 2 more pan drains?

Trans temp never gets over 200 and I very rarely pull more than my lawn mower on a random utility trailer. It’s mostly highway runs but it does idle a lot.

Looking for ideas.

What fluid did you use last time? You can pull a cooler line and start it and pour fluid in as it pumps it out until you see fresh fluid.

I’m not sure. It had 37,000 miles on it and I bought It from the a GMC dealer who said they had replaced all the fluids. I specifically Asked about the trans. So I am assuming dex 6 but IDK for sure.

I may try that as a fluid exchange. Good idea.

Converter and pump is about to poop the bed. The converter design frankly sucks and should be a billet. Also, modifications need to be made to the pump to help with the converter issue. Once this is done, they last a long time.

Pm sent 329

AGREE WITH 329L. CONVERTER IS JUNK AND IN THE PROCESS IS RUINING THE PUMP HALFS AND POSSIBLY MORE. DONT DRIVE IT ANY MORE

I don't know anything about the 6L80E, is it supposed to be an improved version of the 4L80E? (Or just 2 more gear ratios, but possibly at the expense of durability)?
My old 2002 HD2500 had the 4L80E, and it was bullet proof, hauling a lot, over plenty of mountains, etc. No issues in 285K miles.
Curious if anyone has the eight-speed 8L90 trans in their 2015 or newer truck, and if it was a costly option, or not a lot of additional money. And would like to hear how those with the 6 and 8 speed trannies like the performance, especially with regard to towing.