Roger,

Your MPG should improve in the summer and decline in the winter. It is just the way things are because the winter air being more dense will require more fuel. The pilots on this forum can look at the performance charts and see clearly that this is the case.

But do not forget other factors. Are you towing? Are you running in more hilly terrain? Do you have a headwind or tailwind? Is your speed the same? Did you get some biodiesel?

I reset my DD Pro Driver at every oil change so the mileage is spread over a 5000 mile range. That tends to average out minor trip variations. I am now averaging 8.3 on this last 1400 miles (to OSH), but I did not tow, so I expect when I do tow, I will pull it down. If we go to FL via Atlanta and we don't go through the mountains I see about a .5 MPG difference from when we run through the mountains.

I think your range is normal.