[spacemanspif]

This is an interesting one from the aspect that you haven't done anything to the car...it just seems to be that way from the factory. My only question would be: are you now driving with traffic? In that maybe its the fact that you are driving in the wakes of other cars who would normally pass you. Driving slower seems to keep me in "fresh" air a lot more than I ever was when I drove 65-75mph.

If you did mods, this next story might mean more but it has the same lesson to be learned - lower RPM doesn't always burn less gas. So my Monte Carlo SS came from the factory with a 305 engine and 3.73:1 rear gears. When it was my only car I wanted to get better mileage than the 15 I was getting because I had a summer job coming up that was going to require a lot of highway driving. I found a rear out of a Malibu with 2.29:1 gears in it (probably didn't have an OD trans) and swapped in the whole rear. Did some math and found that something crazy like 1600RPM was 65MPH. I drove the first 2 tanks at theoretical 65mph and get like 10mpg. Did some reading and found the Monte engine is more efficient in the neighborhood of 2 - 2500 rpm. Started driving faster to get into the "ecoband" of the engine and my economy shot up 25mpg. After doing the some more fuzzy math I figure that I was doing a little north of 75mph but that the car "felt best" a little north of 80mph...either way, I was passing everyone and getting 25mpg with an engine that never got better than 15 for me. I think they were rated at 21 from the factory... Sometimes it doesn't make sense but I wasn't about to complain about getting places faster and burning less gas doing it