22mpg. ALWAYS.

[immortal_suby]

Relax man, I was just kidding with you. Nothing wrong with stepping on the gas, I do it every time I drive. I just don't expect my gas mileage to be good when I'm hammering on the car. If I run through a tank hot rodding around the whole time I'd get around 16-17mpg. I used to drive like that all the time when I first bought the car and I have logged my gas mileage since I bought the car. Not really because I care about the mileage, more so I can tell if something has gone wrong.
Now I get around 19-22 mixed city driving with about half of the time spent racing around and 26-27 highway.

10 mpg is pretty low. They could have screwed up the plugs by not gapping properly but I expect you'd have some roughness in the engine. I'd also check air filter, all the vacuum connections, 02 sensors, and make sure the intake boot is on tight and also the intake itself is bolted down tightly. Do you have alot of black soot in your tailpipe? Have you ever had a CE light? Maybe your crooked dealer pulled the bulb out and you don't know its throwing a code. Have you tried a good fuel system cleaner?