i can easily get 17-17.3 around here (two lane roads maybe some very light pulling) with my '08 3500 duramax reg cab. Hand calculated, figured a tank full at a time, no BS. It doesn't have any emissions equip anymore, though. Haven't taken it on a trip yet to see what its capable of. I get exactly 1 mpg better then i did with my 6.5, both driven the same and the '08 has 165 more hp and 250 ft-lbs more torque than the 6.5 did. Im very pleased to say the least.