Thats great milage! Although my truck is a 4X4 3.73, I have noticed speed seams to make all the diffrence. Pulling a 20 ft. tandem trailer empty down hill at 75-80 mph for 300 miles I got 14.8 mpg. On the way back with a honda civic on the trailer, up hill all the way at 60-65 mph I got 17 mpg. Go figure.