Now, with the further comments about "Deathflash" I will be searching the forum here with that term. I had no idea there was a name for it. So, good to know!

Here is where I am at right now...When in town yesterday, I called Autozone to see if they had an o2 sensor in stock. They do not. I was right near NAPA at this point, so ended up just going there. NAPA is the most expensive place for parts in this town, but all the guys there yesterday were incredibly helpful. A couple of them came out to try and determine if I needed the round connector, or square one for the o2 sensor. We still don't know, even tho the kid was able to reach up and feel a connector, he was not able to contort quite enough to avoid the hot exhaust, and get it disconnected. Clearly, I have a fun job ahead of me here! I ended up buying both available pre-cat o2 sensors, both the round and square connector, and they will buy back the one I do not need. It just so happened that the o2 sensor light came on again during this trip, which pushed me to buy both sensors, and just get it done. Gotta start somewhere!
Now, my hope is, that this sensor is what is confusing the PCM.
And with HeyYou's new reply here, I am gaining more confidence we are on the right track, especially with Michael and Ramman's input as well.

I also got a good look and comparison of a new tensioner pulley, held up to my engine. And discussing that whole thing with the guys there, that could see everything themselves, we all ended up deciding to start with just a new belt for now, and see how that goes.
They did all agree that the plugs, wires, cap looked in good condition. I mean, as much as one can see without pulling everything off, just a simple visual look.

I currently have the little 550cca battery in the truck, I checked it's status once I got home, it was at 12.41 volts. And this is without ever disconnecting it during the 4 hours, and multiple starts during errands, and driving, etc. (it was a 30 to 50 miles round trip) Since the engine was running good, I was too scared to disconnect the battery (like I normally would everytime the engine is turned off, due to some drain somewhere), and have the PCM reset to that bad death spot.
And finally, I want to see exactly how bad this drain is, so I left the battery hooked up for 6 hours once parked at home, and kept checking every hour, to see how fast it drains. It took 6 hours before it went down to 12.39v . Even tho I have a couple of batteries, I decided to not risk leaving it plugged in overnight. This little battery seems to be holding up much better than the bigger one I bought for this truck.

I do think the ground on the alternator needs to be taken off and cleaned, other than that, I still need to crawl around and check a lot more wires, grounds etc.

I did also stop in at the muffler/suspension garage, due to some steering issues. I need a new trackbar.
Luckily, it is not urgent, it is not dangerously falling off yet. It is most notable in 4WD, not really bad for just road driving. That job can wait awhile.

I tried to find a place on the forum (my profile page), to add my signature, so that it displays my truck specs. Can't find it:
This is a 2001 Dodge Ram 2500 5.9L Gas 4x4
Interesting sidenote, NAPA informed me the truck was manufactured in Jan of 2000 That is according to the door panel sticker.