Monday while driving down the interstate I lost overdrive.

The following day I took the truck on a test drive after checking and topping off the trans fluid. It did the same thing for a while then it would come in and out of gear. After another mile or so I could barely get the truck to stay in first long enough to get it off the road.

The codes are:

1757 - Transmission control pressure not equal to target. (Zero pressure problem)

740 - The engine's running faster than it should for these speeds

Can someone explain these codes? I am expecting to replace my transmission but I would like to cover my bases before taking the plunge and buying the replacement.

Any help would be greatly appreciated.

Thanks,
Curt