Just got back from my mechanic who hooked up his computer to my car. There were no fault codes and he assures me that everything was running within specs. I watched the O2 sensor millivolts vary from about 80mv to 800mv. He said that was normal and that meant it was doing its job.
His explaination for my 9mpg was that I may have had the A/C on or that I was just driving it hard. The truth is that I do like to speed away from a standstill and I do accelerate quite often. I guess I'll have to take it easy for a while and see how that affects the mileage. I'm a little dissappointed since I was expecting to get at least 16 mpg with my driving style in city driving.
Anyway, thanks to all for the help.