When I bought my '05 crew cab,3500,dually,Cummins, 6 speed, I checked all the way from Houston Tx. to Vancouver Wa. Dave Smith motors can be beat fairly easily. I ended up buying right near here in Caldwell, Id. at Curt & Hal motors. They beat everyone. I gave 31k out the door. And as far as the fuel mileage, I get 16/17 in town and 18/21 on the highway. If I can keep it at 74mph it does well. You go 75 or over and mileage falls like a rock. And this thing is a beast. I thought my old '96 2500 Cummins/auto was a brute but, this thing pulls a 21,000 bachoe and trailer easy. I did put and exaust brake, cold air intake and straight pipe the muffler for a little added help. I haven't chipped it yet but, I may.