I have an 04 crew fx4, with stock 3.73 gears and currently running 275/55r20 nitto dura grapplers (32" tall and 10.8" wide). im upgrading to 305/55r20 nitto trail grapplers (33.4" tall and 12" wide) i shouldnt have to change my gears right? if im correct its only neccesary if you're running 35" or larger? thanks in advance

 

By the way I have a 2.5" leveling kit (no body/suspention lift)

 

changing gears is all personal preference. You will definitely feel those tires as they are substantially heavier. But you are correct in not needing to changes gears, atleast it not really being cost effective. To save your tranny, you can drive around in 3rd until you get a tune to reposition your shift points or until you get on the highway and need the extra gear.