I'm running 285 70-17r. How bad will it hurt my mpg if I get 315 70 will they fit out lift

 

What kinda gears are you running. Going with bigger tires is gonna put alot of strain in the trans and rear end if you don't have the right gears

 

It's the sport with 5.9. I think is got 4.10 in it

 

Verify what gear ratio you have first.

 

i run 35s with a lift on stock gearing 3:55 and i get about 13 running on 91 hemifever. Also with the help of all the mods listed in my signature. I'll be changing to 4:56 gears soon, your going to notice the lag climbing and off the line maybe not as much if you have stock 4:10. Im pretty sure 35s arent going to fit without a lift either, i had 33's on the stock lift and i had to put spacers to be able to go full lock, so its definitely not gonna clear with 35s especially that wide.