Bill,
IMO, the Digital MSD boxes are more sensitive to electrical interference than the analog boxes. This started when I put a 15 amp electrical fan on the car, and I couldn't make a pass unless I turned the fan OFF. The 63 amp Delco 1-wire alternator made more interference as it put out more current. Then I put a 100 amp Delco 1-wire alternator in thinking the old alternator might be overloaded. I think the 100 amp alternator made more electrical interference at lower amp draw, so the misfire occured even with the fan OFF.

So, if you have a Delco style alternator, especially with high electrical load (fans, water pumps, etc.) and an unshielded magnetic pickup distributor, you might have the same solution.