I'm not happy with gas mileage so far, either. Bought a 2015 3500 V8 SL in August. We are at 3500 miles and only getting around 11 MPG. (Mix of city/highway driving, not aggressive on the gas & breaks, no high roof) I know there's no official mpg rating for these commercial vans but before buying, everything I could find said 13-19 MPG for the NV, so 10-11 is quite disappointing.