[rheavn]

"One, does it make a difference, with the gen running, if you put the main engine on high idle?"

No

"Two, as a quick piece of info, can you temporarily remove the fan belt from the gen motor. You don’t want to run it long this way but it will disable the gen motor alternator."

I can & will and report back the results

"Can you get your voltmeter probe on the back side of the alternator and read the voltage with the engine running?"

No I can't, but I can test voltage at the alternator lug at the battery isolator.