I gotta '06 quad cab 2500 SWB 2x4 and I get 16-18 on the hwy. I put a predator programmer in it and I set the beast loose! My mileage didn't change but I gained about 180 hp & 350 tq. I haven't been beat yet! I'm in the process of converting it to a SWB dually right now. I got the hub spacers and the wheels , now I need a mega cab dually bed.