65 Ammeter now shows overcharge when accelerated

I've seen something like that, too. Usually happened when the battery had been seriously discharged. I'd put mine on a trickle charger overnight. That would clear it up most times. If not, I'd put in a (known good) battery from one of the other cars and try it. Sometimes, I'd skip the second test and go trotting off for a new battery.

I've only had one voltage regulator fail in my life (GM), so I have no practical experience testing one. Those are the only two culprits I can think of besides the alternator.