1997 Ford Ranger Gas Mileage Problems

I have a 97 ford ranger 2.3 thats been having gas mileage issues lately. I use to be able to get atleast 150 miles at half a tank, now I only get 110 miles at half tank on a good day. I took it to get a engine diagnostic done on it and they said I needed a new mass air flow sensor, o2 sensor (before the cat. Converter) and 2 coil injectors, so I went and replaced all those, but the gas mileage still hasnt changed, so my question is, what else could be the problem?