I picked up my '05 K2500HD CC SB 6/13/05. Used 18.895 gallons to go first 270 miles. I will fill up tonight or tomorrow on second tank full. That puts me at 14 mpg on first tank and I can tell I am doing better on second tank. Taking my first trip towing in two weeks. Does anyone use fuel additives? Any recommendations? I heard it's good to use during break-in.