[Ian]

when was the last time you changed the fuel filter? If it's after the pump, that could be your restriction.

It would have to be a hell of a vacuum leak to flat out kill the motor. Most vacuum leaks just make the car run like garbage.

I doubt its a valve sticking, otherwise you'd hear backfires out the exhaust or intake.

Is your car still points or is it upgraded to HEI? If it's HEI, I'd try swapping out the ignition module to see if that does anything for it. If it's points, get a new condenser and a new set of points.

These are just a few simple things that you can try out to see if it makes the car run any better. Good luck with it man.