Bought this truck used, had 55-75 mph vibration from day one. I thought it was probably just tire balance. Had the Good Year Wranglers balanced, but it didn't help. I started reading everything I could on the forums and concluded it could be a number of driveline connected things. I didn't want to start throwing parts at it, although I was about getting ready to start doing just that. I put two new Firestone Transforce tires on the front this morning, and it has smoothed right out. Also had my front end aligned before getting the tires, but that didn't help. I'm very happy to have a smooth ride.