1990 Oldsmobile Delta 88 Problem idling in drive or reverse

I have changed the fuel filter and put STP fuel line cleaner in the gas tank and still my engine seems to be running in very minimal amount of fuel. When the car is idled the engine stays running but sound like its not gettiing enough fuel, but once it is in drive or reverse, the engine wants to stall out, in order to prevent this i have had to press the gas and brake at the same time keeping the engine running. You can really feel the car's engine having trouble when its about to die, it will virbrate the car when at stop light and when just started or in drive and reverse. Is it possible that their is a lack of pressure in the fuel line, like a tiny whole or something. or even the fuel pump. For the most part the car will stay running but im afraid if this problem is left unresolved then it will reap major problems later on