I have a 2008 2500 4X4. Lately the rear tires have been wearing on the inside and out side edges. I replaced the wheel bearings and seals. Then I put on a new set of the same tires. Still the tires wear the same. I have 373,000 miles on it. I am using Michelin LTX ms2. I haul heavy loads so I keep the air pressure at 80 psi on all 4 of them. Makes for a rough ride but trying to save the tires. Could it be shocks or bushings in the leaf springs? How hard are the bushings to replace? Thanks for any help.