Yanyfan100, I live in an area where the traffic is light and the speed limit going to work for me in 35mph. As for the rpm's I have an automatic and it usually does not exceed 2200 even when I am accelerating. Also I have always used mobil 1 full synthetic oil since I bought the X back in 02. Maybe that helps with engine wear and efficiency? FYI when I use to live further away from work and would run 75-80mph on the HWY my mileage would be 17-18.5. It seems my X is very sensitive about mileage especially at higher speeds.