I've been averaging 16-17 mpg. The worst was 10 mpg while towing a trailer. The best was somewhere around 21 mpg when it was still stock. The front bumper and lift lowered the mpg because it worsened the aerodynamics around the front tires.

lynchknot - yes, you have the last year of the 3rd gen 4Runners.

I expected some improvement in mpg when I installed manual hubs a few years ago, but it was essentially a negligible difference. Manual hubs for 3rd gens basically aren't worth the trouble for the large majority of people. They cost about $1000 if you find a decent price for the full kit, like what ORS sells. You have to replace some major pieces, including the front axles, front wheel bearings, hubs, and other parts within the spindle. I saw value in it for myself in other ways due to hard off-roading, such as if I destroy the front diff with the front locker, I can still reasonably easily get off the trail in 2L. It is nice that my CV boots last longer with the manual hubs. (Now I just break the axles before I need to change the boots).