I have 4000 miles with a stock CC dually. It gets better every tankful. My '04 seemed to get just a little bit better (identical truck) but this sure cruises better at high speed. Love the 6th gear. By the way, figure the milage by hand, it actually comes out better than the computer. The computer figures it burned 30 - 32 gallons for an approximate milage of 16 but it only will take 28 - 30 for a milage closer to 17 - 18 mpg. The computer figures it burned more than it actually did.