Loss of power on my 95 bonneville. No real pick up whatsoever?

The loss of power sucks...My car sounds like its sputtering, and the only time it seems to have any kind of pick up is when the car is cold or when im at 50mph and above and thats with me slowly pressing on the gas,and even then you can hear the sputtering. I've replaced the fuel filter, no change. I've checked the catalytic converter,and its not glowing red.Sitting at idle the engine sounds ok.Im starting to think its either a leak in the exhaust manifold or fuel pressure is low, but would that cause the engine to sputter when pressing on the gas?Please help