Here'* the Crux of the matter; the Bonneville was not behaving this way on a Monday, then on Tuesday is was. There must be a reason why.

Okay Gents, this is where things stand:
Today, got back to trying to figure out this voltage issue.
This is what I did; I made myself some leads long enough for me to run my test leads from the B post on the Alternator and a solid ground into the passenger compartment so that I could monitor the voltage on my Multimeter.
Tested battery before starting, 12.62 Volts, good to go.
Started Bonneville, 14.1 volts cold, good to go.
Allowed the engine to come to running temperature, 13.5 volts, good to go.
At running temperature, shifted in Drive, 13.35 - 13.45 volts, seems good to go.
Shifted back to Park, turned on A/C (blower on high, radiator cooling fans came on), Lights on, radio on, 13.25 - 13.35 volts, still seems good to go.
Under that load, I shifted into Drive (foot on brake, of course), volts drop to 13.15 and from there, I watched the voltage drop over the next five minutes or so to 12.45.
Summary, running temp, under load, shift into Drive, voltage drops during that five minutes from 13.15 to 12.45, gradually.

Any thoughts?

You may want to put in new battery cables; I have had cables go bad with no outward signs of problems with them. They are not that expensive, and at least you can rule them out as the culprit. And as mentioned - clean all the chassis ground connections with a wire brush or sandpaper and consider new eye hooks on those as well. Also, may want to swap out battery to rule that out as well. I'm a battery weirdo and have additional batteries I maintain with trickle chargers.

The Regulator performs as it should while the car is in Park. The Regulator FAILS when shifted into Reverse or Drive. Now, I am wondering about the PCM. I need to perform a Continuity Test on the Red and Grey wires leading from the SFL plug.

Has this ever happened to anyone?