alright, so i do a lllllot of fwy driving and want more power/mpg. i have an 04 screw with the 5.4 but got stuck with the 3.55. i do a fair share of city driving too and lose my **** on mpg with 3.55s. i know if i went up to 373s i would get better mpg, if i went up to 4.30s would i still see a gain in mpgs?

 

If you stay with the same tire size, going to a lower (numerically higher) gear ratio will make your truck more efficient around town, but at highway speeds you'll probably get a loss in mpg. If you do a lot of highway driving with the stock tire size, stick with the stock gear ratio.

 

well im aslo goin to be upgrading to 33s in the very near future, maybe get a lift and throw 35s on, im always thinking about the future haha

 

If you're definitely going to 33s then I would regear to 4.10s. That should put you right around stock RPMs. If you do go to 35s after that then your highway mpg should actually increase, while your city mpg will go down slightly. Basically, if the majority of your driving is city, go with a numerically higher ratio. If the majority is highway, go with the numerically lower ratio.