Hey ND, I had the same problem and it was the speedometer cluster that just went south. Check all of the other things first (espicially connections), but if all else fails go to the junkyard and pull one from another truck or ramcharger. Very easy to change out, but you do have to remove the entire gauge cluster to get to it. I forget where I got mine but I bought the entire dash cluster (all gauges) for $45. 00. Everything is on a plastic circuit (sp) board much like a computer motherboard. Once it was in everything returned to working order. Good luck.
Shrimpy