Problem?????

what are the cam specs? idle speed? rear gear ratio? torque converter stall speed? vacuum readings?

This could be because of a dead cylinder. Other symptoms for this would be black smoke out of the exhaust. If you have a catalytic converter on the car it would be glowing cherry red due to trying to burn off the excess gas.

To narrow down this as your problem you could unplug plug wires one at a time and listen for changes in RPM. If the cylinder is working correctly you will hear a drop in RPM. If you do not hear a change then the cylinder is likely dead.

Pull the suspected dead cylinder's spark plug and look at it. It will be excessively black/brown.

Another possible cause is likely to be a vacuum leak. If you have a vacuum gauge you can hook it up to a manifold runner and take a reading off of that. Depending on the cam you are running and what not you should be in the 17-21 inHg range or more.

A vacuum gauge will also help you narrow it down to a burnt valve etc. Here is a link to what I am talking about.
On Fire

Sounds like a vacuum line is off somewhere. Check all the vacuum connections carefully, and I bet you find one off.

Is the firing order for a 302 or 351. Check the cam card and make sure you have the correct firing order with the plug wires.

Did you measure or check your push rod length? Are you using the stock rocker arms?