I have a 2008 SR5 4x4 V6. Stock it would get about 20 around town and about 22 on the hiway. Now that I have lifted it and installed slightly larger tires it gets about 18 in town and 19 on the hiway. Hand calculated. Although, this time of year I also let it warm up a little first so that isn't helping the mileage either. Hope that helps.
I have an '08 SR5 4WD V6 also. Stock, I got around 18-19 around town (mixed city/hwy), 21 all highway. This was with the Dunlop AT20 tires.
Switching to 255/75 Goodyear Silentarmor tires, the mileage went down about 1 mpg. I think this was mostly due to a more aggressive tread than the height of the tire. (I think that switching to
any tire other than the no-traction Dunlops would cause mpg to drop.)
In fact, when I use 265/70/16 snow tires in winter, mpg is slightly less than with the 255/75/17 Silentarmors. Some of this may be due to winter gas formulations.
I recently added a small leveling kit (Bilstein 5100s at the ~ 1" notch) -- made no difference in mpg.
I live at about 4700' elevation, and rarely have long/ flat/ constant speed highway drives, so I expect my mpg is at the lower end of the spectrum for similar 4Runners.
BTW, always regular unleaded, never premium. There's also always a Yakima rack on the roof rack, with bike racks (summer) or ski racks (winter) further affecting aerodynamics.