I think the rpm jumping on the tach is just a sign that the distruibutor was messed up. If I'm right, the Tach gets it's signal from the distributor. So the distrubutor was messed up and sending a crazy signal to the tach (and probabaly a crazy or intermitent spark to your plugs). If I were you, I'd drive under 3,000 rpm until you figure it out because is sounds like whatever is wrong is frying the distributor at or above that rpm.