welcome to the Org bud... most will tell you that 17mpg is very damn good.... also is this hand calculated?
lil cheap things you can do to get better MPG is keep your filters clean... this includes your air and fuel filter... make sure your tires are properly inflated... the biggest factor is your right foot...
now if your willing to spend some money a 4" TB exhaust will create less restriction esp if you elliminate the cat and exhaust... and i would highly suggest a custom tuned SCT xcal 3 with an econo tune....
let us know if you have any other questions and welcome
-Raul