Since you have misfires and sluggish performance. It's time to check the plugs and the fuel pressure both running and when shut off. See that the pressure comes up to the proper level and that it stays there long enough after being shut down.
If you find the plugs are all fouled on one entire side of the engine, you know the problem is fuel related. If you find less than 4 fouled, it's ignition related.
The fuel pressure regulator is located under the plastic plenum. If the diaphragm is ruptured, it will leak fuel into the intake causing rich running and misfires.
Pressurize the fuel system after removing the plenum. You will have to disconnect and reconnect the fuel lines. They bolt on the top and at the rear of the intake. Be sure to check all the connections for leaking under pressure.
While there, also plan on replacing the gaskets between the intake and the heads. I believe these gaskets are different than the crappy plastic ones on there now.
http://store.summitracing.com/partde...5&autoview=sku
You'll see those old intake gaskets are not worth a flip.
There are a few other things you will want to check and at least 1 you will now NEED to check.
The rotor and cap need to be changed once per year. Despite what you may have read or heard. Check them for signs of white corrosion.
If the wires have over 50K on them. Change them also. Brand name only.
If the O2s are older than 60K, change them. Don't use Bosch. OEM only.
If you have been running rich, need to check the cats if you still have them. Running rich screws them up big time.