Originally Posted by Karls03

I just scan read over this, so forgive me if this has been offered: have you hooked up to the OBDII port under the dash on the driver's side to check for fault codes? 13mpg on a stock 6.0 is ***! I live at 4000ft and got 14~15 stock on 33s in town. I get 13 on 35s right now. However, when I go to a lower elevation, Vegas (2000ft) or Phoenix (1300ft) I get mucho bettero mileage! Like 15 in town on 35s.

But I digress, check your codes, THEN worry about upgrades.