I'm about to step up from stock 31 inch tires to 35s on my 07 Sahara unlimited 2wd. I already put in 3 inches of lift but I don't know if I should regear. The dealership says they can't fix all speedometer problems and power/mpg issues by computer...is this true?? I thought I need to regear the back differential

 

You wouldn't have to regear but it'll help you get back the power you will definitely lose going that big of a tire. I would suggest a 4.88 if you do a lot of highway driving, 5.13 if your more of an offroad driver. And you need to do both axles, otherwise your going to destroy your transfer case.