I get 15mpg in my '08, after it's been adjusted for 32" tires, and running 3.21 gears.... 2" lift, steel bumpers, winch, gear, etc. (lots of extra weight)
With an automatic, like LB said, using a computer flash will help with both your tire size and your "shifting", and if it's not calibrated already, you'll see a HUGE jump in perceived mileage. 15mpg in a 4dr with 35's is pretty darn good, though....be happy Atlanta's pretty flat:-)
I'm just here for the gasoline. --Max
If you aren't recalibrated for the tire size and if you haven't regeared that is where you should start.
i have a 3 inch lift and 35's and regeared to 5.13 and I typically get between 15-16.5. Over the last year my calculated average is 15.5. I drive pretty conservatively but cruise at 75 on the highway daily.
So, you really aren't too far off. I didn't see a huge jump in mileage regearing but it is much nicer to drive and my transmission temps stay lower.
The intake and exhaust probably provide no benefit to efficiency in these computer controlled jeeps.