I just picked up a 2012 2500 NV HD SV hightop with the V6. I have less than 1,000 miles on it but had to drive it home from the dealer which was a 400 mile trip. On the highway, I got a little more than 17mpg with the air on. Around town, I am averaging about 15.5 mostly with the air off as it's starting to get cooler around here. I am hoping that it gets better once broken in.