Gas mileage 225 Slant 6

Most of my driving has been around town lately and when I do hit the freeway it's almost all accelerating (I have a 14 mile commute, split between four different highways and 4 miles of surface streets)

I am averaging a hair over 20mpg, verified against GPS, always using the same gas station. Generic 87 octane with 10% ethanol. 225/904/7.25"/13's