Alan:
This can be a very difficult problem. Lots a great advice you're getting, I always learn a lot from theses type of posts. Hopefully you will let us know what the resolution was. Just a thought, if you have points, have you checked them? Also, could there be some type of contaminant on the underside of the distributor cap (grease, etc. that could conduct electricity)? I'm assuming you changed the distributor cap before the problem. In any case, sometimes it is something simple. Good luck.
