V6 4x4. I got 24 MPG. I was driving through a Wisconsin Snow Storm on the Interstate 90. The fastest I would go is 50 MPH...LOL. The RPMS were at 1500 about whole way which was a 5 hour drive that usually takes 3 hours.
On a 7k+ mile trip around the US in our 4.6L 2wd we got an overall average of 22.8 mpg, expressway and state highways, mountains and plains, city and rural generally driving the speed limit. Best was one day in flat central Oregon at the posted 55 mph produced 25.6 mpg.
I was getting pretty consistant 17 all around and 20 highway (on 267 mile trip to Maine).
Then I found something called a hydrogen cracking system on the web, bought the materials and made one and installed it. My mileage went up 18.5 % (to 20.1 all around and 23.7 on the same trip to Maine). I used this system for a few months, then the 45K mile service came due, so I took it off (so they wouldn't give me attitude about possible warranty voiding issues) and I have not bothered to put it back on again. It got to be a pain it the butt adding 6 ounces of gas to a "bubbler" every two days. There isn't enough room under the hood to build a bigger one.
So I am back to 17 / 20 using premium fuel.
best ever MPG was when i was making road trip from Atlanta GA to Toronto Ontario Canada. it was 1000 miles one way.
i was putting 55mph locked with cruise control and got almost 29 mpg
i was able to go 570 miles with one tank of gas. when i speeds up to 65mph it drops to about 25mpg and about 500 mile per tank. i was shocked.
i loved my 4x2 so much. So we bought another one 4x4 v8 limited.
on daily driving 50 highway 50 city 4x2 averages about 20. 4x4 averages 18..
so far my 4x4 has 90000miles and drives like new. 4x4 has 65000 miles and also like new.
only problem was occationally automatic tilt telescoping steering wheels stuck on lower position and not moving up... so i am not touching the ajuster.