low fuel pressure shuts off while idling

when the car is in gear it won't idle it'll shake sputter then shut off. while driving there is now power in the bottom end and not enough power to drive up steep hills. I thought it was the fuel pump at first affter testing the fuel pressure and replaced it but it did not work. i replaced the injectors and that did not work either i can't afford to just keep buying parts or take it to a shop any help or ideas will be greatly appreciated