1996 Oldsmobile Cutlass car jerking

Engine Performance problem 1996 Oldsmobile Cutlass 6 cyl Front Wheel Drive Automatic Hi. I have a 3.1l engine in my 96 cutlass supreme sl that jerks bad. It jerks when im on the gas but it really jerks when im at a constant speed anywhere above 40 mph. also the code I have said that the #4 cylinder was misfireing and I seen fuel leaking from the fuel pressure regulator. can you help me, I have already changed the spark plugs, spark plug wires, ignition coils throttle position sensor, idle air sensor, air filter, fuel filter, and both o2 sensors. I need your help!