1991 regal problem

Ok my dad has a 91 regal as a winter car and the car will run fine for a couple days then it will just die..You gotta hold the gas to the floor to get it to start then it will run fine for a while and do it all over..The computer, the injectors, sensors, sparkplugs, wires, fuel pump, have all been changed and its still doing it...Does anyone have any ideas of what could be causing this because we are completely stumped..Any help would be greatly appreciated. thank you

sounds liek a bad fuel filter or fuel pump.... mine has never broke and ive owned it sicne new so... dont really kno!

Who's is stumped a repair shop or you folks? Any check engine lites, what is the fuel pressure when this happens, only at idle or slowing down? Give a complete description of how it happens and how long it takes to restart, does it stumble or buck when dying and or restarting? 3.1 I assume. Also sensors, what sensors? See where I am going here, info is all important.