I get much better mileage by driving my Focus wagon as much as possible.
The Gibson exhaust on the Trac seems to have added 0.5 mpg.
Not much you can do other than keep it in tune, clean filters, proper air in the tires. There are other mods such as exhaust, intake, tuner, but don't forget to look at the payback period.
I lease my trucks for three years and 45k. Assuming the 0.5 mpg holds true and gas at $3.29, I will save $330 in gas, or about what the exhaust cost.