At a total loss for an explanation
Wow!!! 25 responses. Y'all have been working on this harder than me. I will not be able to get back to it again until tonight.
Things I already tried--not all aimed at fixing this problem: New ballast resistor. Swapped coils with my Roadrunner. Checked spark on every cylinder with a timing light. Pulled front of engine apart to make sure chain was not jumping. Replaced a worn out battery. New fuel filter.
I will be trying a few suggestions this evening. Thanks.