As detailed as this was, you gave no information as to the type of ignition system. Is this Mopar ECU, Pertronix, MSD or some other?
One of the first things I'd do is make a few test runs with the ignition hot wired in order to bypass the wiring harness and ignition switch. If the system uses a ballast resistor, do not bypass that. "Rig" a clean safe way to "hot wire" the ignition and make some test runs
Depending on the type of ignition, there are some tests you can do, but we need to know what type the ignition is
It's possible EG, that this could be as simple as a loose / bad connection, or a tach wire shorting /"pinched" on the way to the tach.
