I had a chance to follow the same route on a trip to Las Vegas recently. For my highway mileage I got 27.1 mpg over 361 miles of mainly highway driving cruising at about 75 mph. Oddly enough, over 178 miles of city driving, I got 30.5 mpg. And on the return trip, I got 27.2 mpg over 296 miles of winding road through Death Valley. Over the entire trip, 835 miles, my fuel economy was 27.8 mpg, less than the 30 mpg combined the EPA predicts.
i think they be a driving fast and paying for it in mpg, most of the posts do not indicate driving style or speed.