messing with the final drive is going to mess up the mileage on the highway also will affect the smoothness, I was thinking of the tranny as it will add one more speed to accommodate the difference. isn't the EML electronics the same for both trannies? or I would need a newer DME + EML ? I already now that I would need a different tranny ECU.
I already have the 3.64 I guess the US rear drive ratio and my top speed is already 265 @6000 RPM still I feel that lower ration 1st speed will solve the problem with a normal rear drive ratio even if I go down to 3.20 Rear drive.

I guess that's a good project to think about to retain a nice smooth highway drive and a powerful pickup from low speed.