Hoping that with all of the knowledgable folks in this forum I can resolve this issue.

I have a 1999 Blazer 4.3 Automatic Trans. It was running fine and I have done a lot to it including trans fluid and filter. It developed a crack in the radiator tank so I replaced the radiator with a new one, after about a half hour of driving I noticed a issue with upshifting from a dead stop. It will shift if I wind it out to 2500 rpm and let up of the gas. Changed the Throttle Pos Sensor and harness. Still after driving about a half hour it has a problem with the upshift from a dead stop. It upshifts fine if I do it manually and there are no other shifting issues. When it is cold it shifts just fine.

The fluid smells fine and it is circulating through the radiator cooler.

I would greatly appreciate any help or suggestions I can get.

 

Mine is doing something Similar. From what I've been reading possibly the shift solenoids. I'm going to try and replace those and see how it goes.

 

let me know what you find out. so far i have traced all wires going to transmission and transfer case also replaced speed sensors and changed complete valve bodys from a transmission that worked fine. I seriously have no clue why it is doing this. I have owned this blazer since 2012 and have only put about 400 miles on it.