Did you drive mostly in city or highway? My 05 GP base model get pretty bad gas mileage in city driving. I got about 16-17 miles per gallon in city, which is around 14-15 L/100KM. My trip is usually 3-4 miles to work so I guess it is pretty bad for gas mileage. But when I go on highway, I get 27-28 miles per gallon (8.5-9 L/100KM). So if you drive mostly short city trip, 16L/100KM is probably not that bad. I supposed gas mileage on 02 and 05 are not that different.
It could be the aftermarket MAF sensor. You can try AC Delco MAF to see if it helps. You probably can get them from Amazon or other online retailers for not too expensive price. If you have a code reader that can show live data, you might look at the fuel trim, air fuel ratio and other related stats of your car. This might give you some insights into the gas mileage issue.
