Engine Stumbling

Okay, we're back. This is from the 98 DOHC engine.

I have since replaced the Fuel Pump, Filter, Plastic hoses from the Fuel Pump, replaced the wires, plugs, EGR Valve, EGR Valve gaskets, all other emission control items seem to be working, and I replaced the hoses running from the elbow under the intake manifold as the hoses had melted so I didn't have EGR or Fuel Pressure regulator control.

However,

Upon going up my hill the car continually acts like it's not getting the gas and also idles rough. There is a faint odor of gas coming from the rear, and I did replace the carbon filter element in the rear, as that had fallen off, though I wasn't able to use a new one, as they don't make them anymore. When I sit at a stop light the engine rumbles as if it's misfiring, but no SES light has appeared. The SES light did throw out a code 420, but I surmise since the engine was running rough that this code is a result of that, not the cause.

There is no smoke coming out the exhaust pipe, and you can't smell unburned fuel in the pipe, just in the general vicinity of the car.
The car runs down the highway just fine, it experiences heavy hesitation while in the 30-40mph range, while running at 1000-1500 RPM. You have to give it more gas to get it to not run rough, but it doesn't throw out any hard line codes to fix. I'm at a loss on this one.