Yea its going to Hurt it alright. I dident put a lift on mine just bigger tires. it has the 5.7 in it and its 4 door. I got 16 with the stock tires on it. Now i get 13.5 to 14

You know i thought about that.. The computer is set for stock, so the spedo is off which would make the MPG display off too.. I reset the trip computer when i filled it up last night so ill have to do some math when it reads empty..