I got a 97 3500. I put a new trans in it last summer. Last fall, i would drive at about 60 mph and the trans would shift in and out of either OD or 3rd and 4th. I put in a new TPS and it stopped doing it. Now its doing it again. If i give it gas at 55 mph, it will shift normally, when i let off at my desired speed, it will downshift. Anybody here of something like this before? I heard of adjusting the throttle valve cable, but i need to know before i screw with it.