i have a 3.42 in my 2011 5.3 liter silverado z71 . Now I am wishing i got the 3.08 gear for gas mileage. How does changing tire size effect axle ratio? can i get a tire size that make my truck act like I have a 3.08 gear in it. my last truck was a 2wd 5.3 liter with a 3.08 and got much better gas mpg. I know having a 4x4 crew cab vs a exted cab 2wd will effect mpg. but not that much. any thoughts?