I have a '05 F350 sc dually I bought it in July of '09 with only 12,700 mi. on it, at the time I was working in Indiana and driving around it got 14-15 mpg. and when I drove it home the lie-o-meter said 18.3 and when I did the math I came up with 18.4 so it was close and I was happy. Back in Ohio I did not drive as much on the highway and over time the log would read 12.5-13.5 and I thought that this was normal. I just went back to Indy and when I left the log read 13.6 so I thought that by the time I got to Indy it would be back up to 18 but the best it said was 14.1. So what do you think? it seems to run fine,the only things that have changed are that I have a tonneau cover on it and the turbo has been replaced by the dealer.