I was wondering if anyone could answer this question? I own a 2004 f150 screwcab 4x4 with 3.73 gears. I have installed a 6 inch pro comp suspension on toyo 35x12.50x20, I do alot of highway driving and possibly will be changing tire sizes in the future to 36 or possibly even 38's but this would most likely not happen for a while. Would changing my gears to 4.27 or 4.56's help with power and gas mileage? Also installed is a 1714 super chip that seems to have help with power. Info appreciated.

 

Welcome ! 4.56s will put you near factory performance and mileage with the 35s. 36s and 38s with 4.56s will start the doggy process all over again. 4.56s would be my minimum choice.

 

i agree with max 4.56 for 35" and 4.88 for 38"