Just go to the dealership and tell them you need an Encoder Motor position sensor for your truck. Its a servicable part. I put them in pretty regularly. Its about 100 bucks though. All you have to do is pull the front D shaft, take 3 bolts out that hold the encoder assembly on, unplug it and take it off. Hope the heck the shift shaft seal isn't leaking and then tear the encoder assembly down. IIRC all you have to watch for is the timing of the gear set. IIRC there is a timing mark stamped on the big gear and then a timing mark stamped in the encoder housing. The small pinion gear I guess you could call it doesn't have a timing mark on it. Just make sure you get the encoder sensor seated in the housing good and then big gear seated into the encoder sensor good. Also get a new gasket to for the encoder housing. You don't need a new gasket I guess you call it where the encoder bolts to the T case, just where the two halves of the housing bolt together.