Well, gas mileage is great compared to my '97 F250. The 5.4 in the Navigator does much better than the 7.5 in the truck! Probably 90% of the vehicles you can buy will get better mileage, so if that's your sole criteria you'd do well to look elsewhere.

I've found my Navi L can do lots of things that those other 90% can't do, so I feed it plenty of the cheap stuff and move on.

As far as off-roading, I suppose it depends on what you want to do. These are big buses, especially the L's, so navigating (ha-ha) narrow trails like a CJ or Wrangler ain't going to happen.

The Navi's don't have low range either. But first gear in the 6-speed is plenty deep, so I don't think it's an issue. Also, it's not like you'll be slipping the clutch to get it going.

The traction control is brilliant as well, so I think you'll be able to go places you fit, even without a locker.

Ground clearance... if you have the power running boards it might be a hair better between the wheels than an Expy that doesn't (Expys could have power boards, but try to find one.)

So, hard-core rock climbing? I don't think so. Getting to the cabin, or scouting through some fields? Don't see why not. But put those chrome 20's away and find something more trail approriate. Though far from identical, here's alot of F150 underneath these.