I'm getting 15.5 mpg, long term average, on mine. 5 spd, 1999, bumpers, sliders, armor, TC doubler, winch, 3" lift, 1" body lift, currently running 33" tires.
It does get better MPG, as you'd expect, on long road trips, but I tend to drive a bit slower on long interstate drives than I used to, simply because the truck has to work harder. So instead of 75 mph out west, it's 65. in town, esp doing shorter trips, the MPG is worse. Takes a lot of work to accelerate the thing back up to speed over and over.
Another thing to consider is that you need to correct the odometer reading to get a true apples to apples comparison of your before and after MPG. I don't bother, since I'm not really concerned with the MPG number, just in spotting odd drops because of some looming issue. But the 4Runner gets its speed info from the ABS system, which is counting wheel revolutions. This means it isn't affected by differential gearing changes (nice) but it is affected by tire size changes. So bigger tires do use more fuel, but they also lower the odometer miles and will reduce your MPG in an artificial way.
Stock tire size for most 4Runners (16 inch wheels) was 265/70/16, with a roughly 30.6" height, 96.2" diameter. You didn't say which specific 33" tire you have, but circumference of a 33" tire would be 103.7". That's a 7.7% increase in circumference, so the odometer is going to read 7.7% less per actual distance travelled. Not to say the odometer is incredibly accurate to begin with, but that's how much it will change. You drive an actual 100 miles on the road, odometer will show 92.8 miles. It's not a big difference (13 mpg vs. 12, more or less) but it's part of the drop.
