Car hesitates

I have a 1994 Olds 88 Royale with 200k on the 3.8L engine. It was hesitating while driving as I would lighten up on the accelerator, but not while accelerating or climbing a hill or otherwise under load. It does it at various speeds, incl. On the highway. I replaced the plugs, wires and one ignition module that had corrosion on it and also the inline fuel filter near the fuel tank. While starting it after replacing the fuel filter and revving it in park it would hesitate for a second every few seconds. I hadn't suspected a fuel pump problem before, but now I am. Could it be a pcv valve? Could it be a fouled or plugged fuel injector? A sensor? Or one of the other two ignition modules? ( I doubt it, since the old plugs looked good except for the one that was connected to the corroded module terminal) And can having the fuel cap loose cause it to hesitate while revving it in park? Any advice would be greatly appreciated, since I'm on such tight purse strings. Thank you. Gary C.