hi, Dan here. i have a stock 06 mega cab. 5.9....I know all these trucks are beasts even stock, however my question is will 35" tires....(pro comp) extreme terrains hurt the truck with the gears it has stock? And also are pro comps going to hurt the diesel mileage? Im very happy actually with the mpg's with the 35 inch tires on it now....(bought it that way) but its time for new ones and I wan to make sure I have this truck for a while...it has 178.000 miles on it....Drove it home back east from Texas.....Love it and dont want to hurt it....thanks guys....dan.....oh its a standard shift......

 

You will be fine, but over time the bigger than stock tires wears out the tranny faster and front end parts . at the milage you will be due for some of these items , unless they have been replaced before you bought the truck.