Volvo: gas mileage on my volvo 99 glt v70 wagon, o2 sensors, transmission timing

Question
I moved to Portland, Oregon from a small town in N. Calif. about 3 months ago.  Since arriving, my gas mileage has plummeted to 13-15 mpg in the city, while on freeway long distance, it's still 26-28 mpg. It used to get at least 18-20 around town for short trips when I was in Calif. I've take it to 4 different places, including the dealer, who have changed both the 02 sensors, but otherwise, they say everything checks out on the computer.  If it doesn't show up on the computer, no one uses their brains.  Could there be something wrong with transmission, timing belt or turbo that would cause the mileage in town to be so low?  Any suggestions.  I've tried different gas at different stations and high test; that didn't change a thing.  HELP.

Answer
Hello Terry! Gas mileage is very tough to keep track of accurately. It all depends on driving conditions, the tyoe of fuel you are using and even the altitude of where you live. If all systems are showing normal and the check engine light is not on, I would have to assume that you mileage is being affected by one of the condtions I have just listed. What was the reason for replacing the o2 sensors? They should have not replaced them if no faults were present.

Jimmy