Stock all season tires on aluminum wheels with 3.73s will net you way better mileage on the highway that a set of mud terrains on steel wheels with 4.10s, the difference wouldn't surprise me to be more than 100km/tank. 2wd would be another huge advantage.
My '09 has been averaging 15 - 17 mpg depending on how I drive, and I usually drive slow. My commute each way is 40 km, half being 80 km/h rural roads and half with the cruise set at 90 km/h on the highway. I usually get around 500 km to 65 or 70 L. The best I have ever got was all highway, driving very easy and I got 19.8 mpg and I was pretty shocked.
A few things to note: I'm 4wd, auto and running 31" MTs with 4.10s and when I fuel up I always top the tank right off until there's gas at the filler hole. I can squeeze around 6 or 8 more litres in than just hanging it up when it first clicks off. My truck turns 2000 rpm @ 90 km/h. I solely use 87 octane Chevron fuel, and apparently they're starting to run 10% ethanol which hurts mileage a bit (burns faster). LR
'09 Ford Ranger FX4 with a mean owner