I had one of my best tanks / mpg wise yesterday and had 359 miles on the tank with about 1/4 tank left. The manual calculation of miles driven by gallons put in equaled 22.5 mpg. The computer was showing 23.4 mpg when I filled up.
As for driving that tank, I drove at least 75 miles in 4WD as I drove over two snow covered mountain passes of 9,500 feet or better. The one thing I was doing different is I kept my speed under 60 mph for most of the day.
I have noted that I get much better mileage keeping the speed down.
No real mods here, just removed roof rack and added C4Fab sliders and about 7,500 miles on the Pro. Oh and I was hauling around at least an extra 50 lbs. of snow and ice stuck to the wheel wells and siders.
This was the highlight of the tank
Since you must be wondering how I got that reading, it was observed about 60 miles into the trip, just after coming down a 7 mile grade out of the the Big Horn Mountains, after having been in 4WD for at least 30 miles, and I had not been applying the gas for quite some time. It took several steep hills for that average to drop down to a more normal average.
Unfortunately, not all of my tanks have been so kind to me. The computer was averaging around 18 mpg while driving across Minnesota and South Dakota, when I was driving 70 to 75 MPH.