Got a 95 3500 with 6.5 td, dually, 4:10 rear end. Mileage is about 10-11mpg no matter what I am doing. Been thinking about seeing if I can swap in a whole new rear end to lower the RPM at highway speed, yet not so much as to lessen its towing ability. Right now I mainly just tow a single car trailer, but might in the future tow a 2 car trailer. Is there a different rear end for the dually that will give better mileage like I am wanting? What should I be looking for?