The rears will wear in the middle fast. If your towing, think about this. If you have 2000lbs on the pin, thats 500 lbs per rear tire. You don't need to run 85psi for that load. It just puts the tires on the center of the tread.
I have LTX's on my truck and have watched this happen time after time dating back to my 7. 3 ferd crew cab. I now run 50lbs in the rears, DC says 55 I believe. Even at 55psi I still have the wear in the centers. Mine are looking better. You should also rotate your tires at least every 10k miles. I saw no differance in fuel mileage at the lower pressure setting.
I guess you would have to get down to 45 or less in the rears if you don't load the truck or tow to get them from wearing in the middle.
Dave