Be careful, some "calculate" or "record" their highway mileage by getting on the interstate, re-setting the display, then making note of it before they get off the interstate.
As any reasonable person knows, one does not calculate mileage in this manner.
BTW, 07 V8 Ltd 4x4 averages about 18 mpg for me. I do a lot of interstate. 14,000 miles so far.