I bought my truck about a month ago. 01' F250 4X4 w/ 7.3l (Stock no CAT). With the first tank of fuel I got 16 mpg. The next tank a little under 16. Then it dropped to about 14, with my last fill up averaging about 12 mpg. I changed the oil when I got the truck and the fuel filter about a week ago. I run Diesel Kleen in the last tank thinking that maybe the injectors were dirty. My driving habits have not changed since I got the truck. My foot has always been made of lead, but I try to keep rpms under or around 2000 as much as possible. Will check the brakes this weekend for drag, but can anyone give me any other things to check? Or, do I just need to take it to a shop to have it checked? The truck has 148,000 miles on it if that matters.