Never thought I'd get excited about something getting 15 MPG! Ha. I have only taken this on a couple of trips and during the first 500 mile break in, I got 13 on the freeway, averaging 70-75 mph and part of this was going in the mountains, by only at 3,000 feet max. I just went on another 400 mile trip with slightly more than half of it on 2 lane roads and the rest on the interstate. The meter would fluctuate and at best it said 17 but right before I filled it, it said 16.2 because a I had a little city driving in there. I filled it and hand calculated 15.5 so that gauge wasn't too far off. I am pretty happy if it continues to average 15 on the highway as those figures of 12 I see had me a little worried. I suppose it may get a little better over time too but I think the important thing may be the speed too. I probably averaged around 60-65 mph most of this trip and rarely got over 70. Does that magic number seem to be 2,000 RPM before it starts burning more fuel? I have the 4.10 rear end.