this last past year i did 3 round trips from San Diego, Ca to El Paso, TX to Dallas, TX and back. On the way to El Paso i was on a time limit of 10 hrs before my grandmother went into surgery. My avg speed was about 80mph (more like 95mph) drive is a lil under 800 miles. From San Diego to Phoenix i was at half a tank and Phoenix to El Paso did a lil bit under half and that was with my 33's. Best advice i have is tunnel, coffee(energy drink) and a ipod and have fun on the drive!!! enjoy the sights oh and give her a good wash before takeoff.