I live in Las Vegas. the roads here are fairly flat. 85-90% of the time I drive around town vs freeway. My truck has 37's and avg mpg is in mid 14's. I have not had it on the freeway for longer than 12 miles at a time, which bring up the mpg, (mid 15's) but not on freeway long enough to see actual freeway mpg. I suspect on a longer trip, like 100+ miles and stay around 70, it would get high 16's to under 18. truck has stock 4.10s