Try reseting your ECU....i was getting about 15 mpg in my 06 azera (3.8) and my car died one day and it reset my ECU and now when i get about 18 mpg.....your ECU get used to how u drive so if u drive aggressive a lot it will just give u gas, gas, gas.....after u reset the ECU drive more laid back for a little while so your gas mileage will stay up.....FYI you lose most of ur gas on acceleration, so don't accelerate hard all the time