Big block 4L80e 4x4 175,000 miles 33"tires. Bought this truck 10'000 miles ago and engine tanny was geat till one night speedometer guit.Then my problem started when you stop at red light and takeoff tranny shifts very hard in 2nd and 3rd gears. When cold tranny shifts like new. After 10 miles it's back awful. Took it to a gm mechanic, he fixed a bad wire going to speed sensor and that fixed the speeometer. But it still shifts bad after warm up and we dont know what it is.

 

I forgot to mention I have already replaced fluid and filter. The old fluid smelt like new and not low on stick. Any help will be appriciated.

 

same here.. just bought it a 169,000 and the same thing happens after we got off of the highway. we had to replace the valve control body(only like $90)(ebay haha) after that.. shifts perfect

 

Ok. lets try this. You need to take it somewhere or if you know someone with a scanner and watch the data stream and see what the computer is commanding the EPC(electronic pressure control) to do. If the values are good, i would say replace the EPC solenoid. I don't think it's necessarey to replace the whole VB. In 12 yrs I think I have only replaced one. Valves just dont wear out in these. Any time a GM vehicle set a code in the TCM, it will set line pressure to max pressure, which 0 volts to the EPC. They do this to try to keep the tranny from burning up and so you will take it to a shop. Hope this helps.