How much drop should there be? The cam is a little lumpy and the vacuum gauge doesn't exactly stay steady.
I already tried a different distributor and I replaced the ground straps when I did the engine. I'll check them though. The battery is bolted to the passenger head anyway, so that should be a hell of a ground already.
Any way I can test the manifold theory before spending money again on a new manifold?
I will try disconnecting the plugs to see what changes.