[Big-Foot]

Hang in there Mike...

I use pretty much all MSD ignition components these days so I can't speak about the HyFire box . The Ballast resistor you have may be causing too much resistance (along with the resistance of the coil) for the HyFire box to handle.
Sometimes there are multple causes to problems like this as well. I had a dial adjustable rev limiter (MSD) so bad once and it would change the rev limit RPM all over the chart all by itself when it got warm. It took a while to find that one too. We were sure we had an ignition coil that was breaking down.

You'll find it - just be patient and methodical in your search.