Problem solved.
Before I purchased anything else I took the distributor cap off to check it and the rotor.
There was my problem. The screw that holds the rotor arm in place had worked its way out and was bouncing around inside. 3 of the contact block in the distributor cap were bent and the end of the rotor was bent out of shape. It's a wonder the car ran at all.
After replacing these the symptoms went away.
Thanks everyone!