Not knowing what engine you have it's a guess that you have the 3.4. Your gas mileage seems to be in the normal range with the driving mix you state. You have to realize stomping on the gas is going to use more...the car itself is 3400 lbs. with 180 horsies strugglin to get you goin...Not a good 1/4 miler by any means. Cats should not be confused with a lead foot. If it were clogged, you more than likely would have sluggish acceleration and around 12-13 MPG! avg.
A. keep your throttlebody and MAF (mass airflow sensor) clean.
B. Air filter should be clean, if not replace it. if you can't see through it when held up to a light bulb it's time.
C. 30 psi is tire pressure recommended by mfg., keep that checked monthly. I personally run 32 front 32 rear. 34/34 on long trips of 300+ miles. I get 34 mpg highway only! 70 mph avg.
D. Use good 5w30 oil and change filter and oil every 3000-5000 mile synthetic can get you 7500. $$$ Biggie Bucks for a non performance car.
E. Enjoy your ride....Dave