The on board computer on the roof is unreliable. It is almost always off. Hand calculate your fuel mileage from now on for accurate results. 23 MPG even in the best of conditions is a stretch, even if your were 2x4 and manual
Those calculations are based upon dividing miles traveled by gallons used. I do use the on-board computer to get me a rough idea of fuel usage data, and will reset to get an idea of mileage over a shorter stretch.
It is 4x2, but auto trans, and 23 mpg was actually easy to get on long trips at 58-60 mph. That's not based upon the computer, but on actual fuel usage. Computer would usually tell me less, in the 21-22 mpg range, but when I calculated it, the actual mileage was better.
I drove to Brunswick, Ohio from Crystal River in central Florida, 1051 miles total, in 2010, and used just 44.2 gallons of fuel, total, for the entire trip up, filling up for only the 2nd time just 1/2 mile from my destination. That's 23.77 mpg. Average speed while moving, according to the GPS, was 57.4 mph.
On the way home, I got only 21.4 mpg.
Best economy ever calculated was traveling from Ft. Walton Beach, FL to Pascagoula, MS and back, where I got 25.1 actual, averaging 54-55 mph. On the way there, the onboard computer showed 27.6 mpg until I got into town. Round trip, I used just 12.6 gallons of fuel. (I log the mileage of every tank of fuel.)
And for the record, it took me 2 years
to learn how to drive it well enough to get over 21 highway mpg on a consistent basis. If you drive it like it's a gas truck, you'll never get over 20 mpg. The first year I had the truck, I averaged 15.6 in town, and only 17.8 on the interstate highway. I still drove 75-80 mph on the highway back then. Now, I know better.
The 7.3 is a very efficient engine when nothing is off kilter.