Put a 50 pound bag of sand in the bed near the tailgate and see if it quiets down. These trucks were designed to ride best with a load in the bed.
I use my '50 3100 to pull a fairly heavy boat and trailer. It is absolutely amazing how that tongue weight on the back of the truck improves the ride quality of this truck.
I am going to determine exactly what that tongue weight is so that I can add that amount of weight to the underside of the bed in the back to see if it gives me the same ride quality and quietness.
