A friend showed up this weekend with a new G-26 in an Extra and it is a good solid running engine with good power and no electrical issues. There is also another one at the field, that is the same.
I still think you may have a vibration issue of some sort. Maybe you should mount the engine in a test stand, and then while it is running, gradualy add electronic components in the proximity to see if you get glitches. Or see if someone has a known good G-23 or 26 that you could borrow to mount in your set-up to see if the problem goes away.