A real head scratcher for the 'charging' experts

[ManzanoNissan]

So my old 1991 D21 4x4 cacked up it's alternator while on route to the city. 40 mile journey and half way there when it happened. Tow truck took me back for 250. Throw the charger on the battery, borrowed neighbours truck and zipped off to O'Reilly's and picked up what seemed to be the only alternator for that truck available anywhere. Worse, refurbished.
Installed it and it was dead on arrival. No charge. I checked the power to the hot wire and got 12.04 so there's power to the alternator...bad alternator.
Took it back to OReilly's and they tested it as bad. No problem they had another in the city delivered to the location and I took that.

So I'm using the truck for a week. I notice at start up she doesn't have a peppy fire up, one you'd expect from a brand new Duralast Gold you just bought a week before the alternator issue.
I take a run into the city and about 28 miles in ... she chokes and dies. Dead battery, not enough juice to power the four ways. Same tow truck company comes and gets me, gives me a break at 180 for a ride home this time.

Charge the battery up again overnight and the test in the morning with the engine on shows the bloody alternator is charging 14.2
I don't take the chance and I switch it out with another Autozone (refurbished) that I had bought but arrived late. Run back into the city, stopping and testing twice along the way. No problems. System charging 14.2-14.3. After a round trip and running around the city to boot, no problems. Battery tested at rest at 12.8

I drop off the OReilly's second alternator. They test it 5 times and it tests fine.

All I can come up with for research is that because it's a refurbished (I can't find a new alternator anywhere online for the 91 D21) there's a possibility the internal voltage regulator is wonky.
I can't account for anything else wrong in the system outside the alternator because as explained above, 100 miles with city driving, no issue's after that alternator was switched out with the Autozone model. The original problem started with the original 30 year old alternator dying and tested as such by O'Reilly's. The likelyhood I've gained a new charging issue at the exact same time the old alternator died seems a bit of a stretch. Not saying that couldn't happen.

So does anyone else have any possible explanation for a battery drain event that isn't caused by an alternator?

[VStar650CL]

With an internally-regulated alternator, the only other things that can cause a "charge crash" are all wiring and cabling. Nothing about the battery can cause it, because the truck would still run on alternator power until you shut it off. Then you'd get a no-start. I'm wondering if you don't have a wiring issue, because you don't mention getting a generator light in either instance. If the lamp is supposed to be working, then maybe the wires in the field/lamp bundle are starting to fail somewhere between the battery and alternator.

[ManzanoNissan]

Lights on the panel are out because I've got LEDS in there. All but one is in correctly so the rest aren't lighting up. Have to go back into the panel and flip the LEDS (switch polarity).
No problems on today's run with the Autozone alternator. Have to use it again tomorrow (client xmas party I'm driving to in a mufflerless 91 D21 swankeeee) so there's another 100 miles to test. I'll run a multimeter on it again as I take her into town.