Have you put a timing lite on it? Check the strobe action. Make sure the advancing is smooth on the balancer with NO missed strobes, No jumping back and forth of the marks, and No skipped strobes. If any of this happens, and you have a magnetic pick-up in the distributor, then the polarity of it is reversed. Flip the wires, reset your timing, verify you strobe-action is now correct, and roadtest it again.