I live on a pretty rough road, so I upgraded to some BFG K/O E-Rated 265/70/17 tires, which are heavy bas****s. I'm now I'm seeing a loss of 3-4 MPG and would like to regain a bit of that if possible. If I re-gear, do I need to do both axles and is 4.56 the magic number or is this overkill? I...