‘21 Pete 389 no cruise or engine brake

Also worth considering is total electric load versus what that alternator is capable of producing. People seem to forget that it's also there to charge the batteries. Hence battery faults or diminished capacity (hot/cold) can really play havoc on dc to ac conversion. That forum sounds like a darn good place to start to avoid a lot of the trial & error yourself.

Ohms Law. Just like car audio, household electronics/electric etc etc.