I had a 99 that had similar problems, I ended up replacing the ignition relay switch right underneath the stearing column. I had lights that acted really funky, I dont know if that would be it or not but you might try it. They are cheap ( I think I paid $15 at advanced). If it doesnt work take it back and move on to the next step.
You might pull your dash apart and make sure your wires are good.. is this a truck that you just purchased or have you had it for a while?