Rpm's are jumping

I have an 84 silverado with a 355, edlebrock intake manifold, holly 4 barrel carb, 700 turbo r tranny and a few other things. I have been driving the truck like this for about a year with no problems at all. Regular oil changes, etc.. Yesterday I got on the road, accelerated to about 2000 rpms, and the rpms started jumping/fluctuating slightly. If I accelerate more, or let off some, it stops. It isn't at any certain mph, just when i get going and maintain rpm.

I had a similar problem and it turned out to be the altenator.

The truck still runs strong, just the small surging of the engine with the rpms. When it starts doing this, if I accelerate, it stops, then gets back into it. Or if I let off, it stops too.