Tonight was the first time this has happend on this truck but when i was going between 30-55mph my 0FF switch for my overdrive started blinking. As I continued to drive all I could hear was the engine reving up and not seeming to find a gear then it would snap in and continue driving. When I got it back on the interstate the light went off and shifted fine. I was only on the interstate for about 10miles and when I pulled off onto another 55mph speed zone it started flashing again. It didn't seem to shift and when it did it shifted hard. I find it weird that I just got it out of the shop for a water pump and then all of a sudden it seems I have transmission problems? Any help out there?