I was driving down the road the other day going about 60-65 in overdrive when my truck running at a high RPM and i started slowing down. I changed the transmission fluid, VSS and added stop slip on advise from a mechanic friend, but she still has the same problem. Any advise would be very helpful, thank you.

 

So... Does the transmission still shift, but slips when in OD (4th)? Do you feel it shift from 1st to 2nd, 2nd to 3rd, and 3rd to 4th? We need some more details.