gears

I have been searching the threads, but have not been able to find anyone with the same symptoms. I have recently had to put a lot of love into my 2004 Envoy. Replacing rad, water pump, compressor and now I am having transmission problems. Fluids levels are high, could probably use a flush...

brand new to the forum!... 08' stock everything w/ 96K miles I would smash the pedal to the medal on the highway (just under 80mph) and very rarely would it try to shift into 1st and over rev. (happened maybe 3 times) well it did it again except now im having problems! 2nd gear itself started...