I have recently noticed a significant change in my mpg with a change in air pressure. After my lift, at the installers recommendation, I was running 40psi. Per the in dash computer (not accurate because I haven't reset it for the larger tires, but useful for comparison purposes) at 40psi I was getting 10-12mpg. I tried upping that to 45 psi and found that my mpg went up to 12-13mpg. For my last trip I went up to 50 psi and got 15-16 mpg. By this theory, I am hoping that at the max psi for the tires (80psi), the car will actually make gas while driving, but I am thinking 50psi is going to be the sweet spot and don't anticipate any further improvements.