My 2500HD bed is 1/4" lower on the passenger side. You can look at the back glass and see the differance. How can you tell if its your torsion bar. I measured the 4 corners of my bed and passenger side is 1/4" lower on front & back passenger side. I was gonna just shim up the bed.
Check your clearance on the front tires to fender wells. The torsion bars are what hold the front of the truck up. If one is off it will be most noticeable on the rear of the bed as there is a straight edge there. The hood does not have enough of a straight edge to notice. If you bought the truck used it could have been used to haul heavy weight and the springs could be weak on the passenger side or the bed mount bushings could be worn on the passenger side. Look into the front end first.