I have a 4th Gen and get 22 plus on the freeway but off-road I don't think it is a great choice, actual I think it is a crappy choice. The departure and esp the approach angle is terrible, clearance is terrible and feels big. It has this traction control crap you cannot turn off. You can't spin the tires in mud, you can't really it bump to get over obstacles. If the tires start to spin the computer takes over and you loose control of your throttle. Maybe there is an override. I love it for on road, dirt roads, light trails and the snow. It works fine for normal driving but it HORRID for more serious off road. Mine is the V6 and the power is great, the ride is great, economy great for an SUV.
It could be lifted and on larger tires and suitable for off roading to an extent. Maybe it is because I own a Jeep Wrangler and had a smaller P/U for off-road before the Jeep but the 4th Gen 4runner just seems fat and awkward off-road and the traction control just ruins it for me. For milder off roading fine but if you need something more maneuverable and capable I just can't see the 4th gen 4Runner as good choice.
look at the nose and butt on that thing (4th gen) even the 3rd gen has a long nose.
here is the 2nd generation 4Runner, much better