My 2001 Double Cab has almost the same mileage. Window sticker when I bought it said 17 city/19 Highway. I added TRD Supercharger/7th Injector.

I've recorded every fillup since it was new --

Max Hiway mileage was 23.6 mpg
Min mileage was 9.4 (pulling a large trailer at 70mph into a 30mph wind...)

Have averaged 17.72 mpg for all driving to date (includes some trailering at around 12-14 mpg)

Average highway mpg is between 20-21
Average in town (16 mile trip on freeway/city streets thru D.C. metro area) is about 16-17.

I can do a bit better if I stay out of the blower <img src="/forums/images/graemlins/lol.gif" alt="" />

(which is not likely <img src="/forums/images/graemlins/kewl.gif" alt="" />)