Thank you M Tangas. I have suspected that the O2 may be the culprit after looking at a variety of posts. The car has 200,000 miles on it and I have no idea when (if ever) the previous owner replaced the sensor. The check engine light comes on frequently around town and goes out after a few miles on the interstate which lead me to think it might be the O2 contributing to the poor mileage.
ABS Ligt comes on frequently as well. Sometimes the check engine and ABS lights do an alternating "dance" with a noticeable loss of power while the ABS light is on. Could this factor in as well?
Thanks for your insight.