Ok, This is really making me maddd! I get this vibration only when my foot is on the gass (in drive). I normally drive in 2 wheel drive. the rear U joints have been replaced, but the tires have not been ballanced, Wouldn't it be vibrating all of the time if the tires were out of ballance, and not just when my foot is on the gass? What else could this be? I know that the front passanger axle u joint has a lot of play in it, yet I don't think I would feel this in 2 wheel. PS, the vibration can be felt every where, in the wheel, in the seat and the rest of the truck. Please help!!! Thanks.