ok so i bought this truck a month ago the seller said he had the tranny rebuilt. (in the process of tracking down his number so i can call him and ask where he got it done again) i noitced after a few weeks of driving it that if i was hard on the throttle it would hit tthe rev limiter before it would shift. so last night i go to put it in reverse than back up a bit than all of a sudden no more reverse. so got the truck to a buddies house and look under it and we pull the rear positoin senor off.. i think that is what it is called it is a black hunk of plastic with to plugs that go in it. . well there is a 1 inch crack in it.. i wounder if water got in there and messed it up.. or if this is even possible to be my cause of my problem?

Manual Lever Position Sensor on the side of the trans where the shift lever goes into it.
If it's bad it can cause drive ability problems but I don't think it will cause no reverse.

Those plugs can be a real pita to remove unless you heat them up first with a heat gun or a drop light bulb.