Some background.Tranny has 180,000 miles.I noticed that it was slipping when shifting from 2nd to 3rd gear.I didn't check the fluid and this went on for about two weeks.It didn't do it every time but 8 out of 10 time it would slip when going into 3rd.
Today it started not working at all.It reved up(was slipping) pulled over and it started working again.Drove about 300 ft and it started slipping again this time it would not move in any gear.This all happened while the wife was driving,so she called from the gas station and i went to check it out.I thought it might have neede some fluid so i checked the dip stick and it was toward the low end on the stick.I added about 1/2 qt started it up and all seemed good.All the gears worked so i backed the truck up about 20 ft then nothing.The tranny was slipping again and no gear worked.The fluid was now in the corect area on the stick and at normal op. temp but still no gear would work it would just rev up.
So i let it sit not running for about 5 min while i thought about what to do.I then started it up again and it was now working so i drove forward about 10 ft and it started slipping,again nothing no gear would work.

So this is where i'm at.If i let the truck sit for about 10 min then start it the gears will work only for about 10 ft then it slipps again and i have nothing.It seems like if it sits it will work if only breifly then it slips.It is acting to me like it is low on fluid but it is not and i have double checked it a few times and the fluid id at the corect level.
The fluid is a bit toward the brown side but it dosen't smell burned like i have smelled on other trannys.
Any idea's?

 

Anyone ever hear of this?
The transmission works for only about 30 sec then it just slips and the engine rpm's rise.I let it sit for about 10 min and the same thing happens works for about 30 sec then nothing it just slips and the engine rev's up.
What could cause this?

 

It sounds like after things heat up, a seal or piston starts to leak past. You really need to get the transmission to a professional that can run through some diagnostics to test the CVI (clutch volume indexes) and see what is going on in the transmission.

It could be something as simple as a worn valve in the valve body which may be able to be honed and a new valve installed or just replacement of the valve body, or it could be a problem with the clutches or pump requiring much more extensive work to cure.