Okay so just ran across this, and I can bet I know your problem. I recently bought a 2d 2007 wrangler X and was getting **** MPG on the highway, even at speeds of 70 mph, or atleast I assumed that speed. One day when I was planning on purchasing some a/t tires because mine came with highway tires, I figured out that the person before me had outfitted my stock 2d with 32 inch highway tires, so whala my solution was solved. My speedometer was terrible off at 70 mph, matter of fact, at 70, I was almost doing 80, which = **** gas mileage. I used my garmin and figured out what I need to do on my speedometer to truly do 65 and 70 mph, now I am getting about 90 miles to a quarter tank, which is way better than 120 miles to a half tank lol.