Originally Posted by Fordzilla80

O.P, is your O/D Off light flashing? How many miles do you have? What you describe sounds a bit like a TC lockup issue. No TC unlock at stops, and problems only start when the TC locks up above 50 mph. Does the truck run fine in the morning? Regardless, you need to pull your transmission pan, change the filter/fluid, check the wiring to the solenoids, ohm them out if you have the ability, and then open up the old filter and see if there's any large metal particles within the filter element. Right now I wouldn't be surprised if either your transmission wiring is messed up, your TCC solenoid is faulty, or your Torque Converter is self destructing itself.

Originally Posted by camodown

^^^

The best answer was given 4.5 years ago. If you didn't listen then, I doubt you will listen now.