I just got a pair of used 245/75 R16 tires from a friend. So I mounted them up on my old aluminum mags and mount the 245's on rear axle of the truck.      They are a bit shorter in height. The gains are great!   Engine load is reduced by 5% to 10% roughly.  EGT's are about 50*F lower. Acceleration is way better and faster.  Cruising RPM's are right about 1,960 RPM at 65 MPH.   I've got to reset my cruise timing limit on the Quadzilla I need