How do i know if i need to change fuel pump or fuel filter

It would not be either of these, but it is a good idea to change out the fuel filter anyway. It is one of the most overlooked maintenance items that need replacing on a regular basis. Sounds to me the engine needs a going over, possible tune up. But there is more to a tune up these days than just changing parts to try and make it run better. The intake manifold bolts should be snugged up, and checked for vacuum leaks, the throttle body should be cleaned, Mass Air Flow Sensor should be cleaned, any trouble codes taken care of. One of the biggest things for gas mileage is the air filter, and the cleaning of the MAF.