I will be getting my truck back tomorrow from a complete rebuild. symptoms very similar to yours. drove it for a while, then it just would never shift into 3rd or above.
sorry, but I agree with Tom....start saving some cash. you might go ahead, if it is cheap enough, and take it to a transmission shop, and have them take a look, and read any codes. you might get lucky and not have to go the whole rebuild route, and get away with a solenoid replacement, or some kind of adjustment.