I have been delivering new trailers and 5th wheels and my mileage has dropped this last trip (5,446 mi) by 2. 5 mpg, and I have no idea why? As far as I know everything is the same and the truck runs fine (2003 5. 9 HO long bed 4X4). I had been averaging 14 to 15 mpg on trips of 4,400 to 6,800 which includes both empty and loaded. Any ideas? Don Chisholm Canon City CO