I would say tires and wheels make a huge difference. Maybe not so much on highway driving, but for normal stop and go, you talk about adding a 33" AT or MT tire, thats an extra 20-30 lbs per tire plus the unsprung weight. That is part of the reason that I have the AT2s, they weigh somewhere around 44lbs, which is almost exactly the same as the factory tire, but I put an extra couple of inches of rubber on the road. I would imagine that the roof rack kills mpg as well. That little 3.5L just isn't enough for a heavyweight VX. I didn't realize that the curb weight is close 5K lbs.