Goobysoobs

i am looking for some serious help. i have a 1996 legacy outback 2.2 litre 4 cylinder. the engine keeps cutting out as if one would think it might be the fuel pump. i have replaced the fuel pump, fuel filter, fuel hoses, spark plugs and wires, sprayed the mass air sensor and checked the vacume hoses. cannot find a vacume leak. fuel flows fine. car ran fine for the last month and the problem re-acured this morning. so now i am at a loss. if i let the car sit for an hour it will start fine but when i put it in gear and give it gas it spudders and cuts out........ any one have any ideas what i am dealing with