I have same stock engine setup with 315 tire set up and leveled frt end. My mileage went from 17.5 to 15. There was a three week period between changing tires and leveling the frt. end. I didn't record the numbers at the time but I felt I lost as much mpg leveling as I did changing the tires or more. I am hoping to gain all that back with a soon coming pcmtune and better than that I am planning to do the "brown gas" upgrade. I got a buddy just did it to his GMC 2500 and got a 45% increase in mpg... I'm getting ready to do it on my hummer.

 

wow excellant job, the grill looks alot better, a nice huge winch on the front of that and your ready to go