4l80e transmission wont shift once it gets up to temp

[cfdlighthouse]

Hello i am new to the forum, i just purchased a 1991 2500 suburban 4x4 has the 350 and the 4l80e transmission. I am at a loss the transmission shift fine when cold, i drive 7 or 8 miles and everything comes up to operating temp and the transmission stops shifting, motor just revs....if i let it cool down a couple hours i can drive another 7 or 8 miles and then it does it again. As soon as its cool shifts perfect everytime till it gets hot.

 

Changed fluid and filter, no metal or sludge in the pan. Fluid was clean and not burnt. Replaced the speed sensors and no change and replaced the two shift soleniods and no change with that either. I just dont understand why it stops working once hot. Its winter time here in va so i can make it almost 12 miles now that morning temps are in the 30s. But once up to temp stops shifting

 

Please help

 

Thanks

 

Dan

[cjb321]

had an old 84 chevy half ton do the same thing once, turned out the pump went out on the transmission.

[cfdlighthouse]

If the pump goes bad wouldnt it just not work at all? Its gear driven so i would think if the tolerances are that off it would not be able to shift like normal at all. It seems to me like once the trans gets hot something electrical is almost putting the trans in neutral

[PondPro]

my 2000 with 304,000 on it does the same thing for overdrive. If it's empty, it usually works, if loaded, I loose overdrive about 5 miles down the road. Codes say slipping, the fluid is basically new-looking. I replaced all the solenoids hoping for a fix, it didn't help. Hope you find yours!