If you're going for mileage and you have a 1:1 top gear (like 3rd in a TH350/TH400) then I can't stress highly enough that you get 2:56 or 2.78 gears. The 2.78 gears are still high-revving for extended highway driving at 70+ MPH. I can just imagine what 3.2x and higher gears are like. Yikes!