My area has lots of foothills (Central Texas) also since I got the truck the A/C has been blowing full blast... My city /hwy average has been about 12.. Most of the post that I have seen here are more than that and most of them were running 4.30's.. Also I have a slightly larger than stock tire which would lower my 3.73's maybe to the 3.55 range (just a guess)..

Also my truck odometer loses about 1 mile per 17 according to a GPS... (that would make for a little worse milage as per the computer..

For example - real world... I reset the Ave Miles Last week - Straight highway showed 15 miles a gal after 43 miles - turn on the county road about 4 miles later the computer read 14.3 - then idles while I open gate about 2 minutes - it said 14.1 - eased up 1/2 mile ranch/caliche road - the computer read 13.4 mpg..

I would think that the 4.30's would have help out the slower speed stuff..