Thought I would wrap this thread up. I let the battery that was on it sit overnight in the cold and it dropped to 11.5V, telling me the battery was on its way out. By the way, I took this battery to Autozone twice and it tested "fine" by their standards, whatever they are. When I brought it there low, they would charge it, then test it.
I put a new AGM battery in the truck ($160 Duracell from Sam's club). I then drove around testing scenarios and in pretty much all of them the voltage was staying higher. I was able to get it to dip below 12 sitting in the car in drive in parking lot for a while with everything turned on, including major bass out of 1000w amp and 15" sub and charging a phone to do everything possible except running the winch. I had to sit longer than any red light or left turn would be. (There is simply no reason to sit in drive that long. When putting it in park or neutral the RPM's go up slightly and it stays in 13v+ charging levels.) Anyway, while sitting in drive that keeps the RPMs a little lower, moving the heater switch from 4 to 3 got it back over 12. So, I coached my son to keep the heater fan on 1-3 once the car is warmed up and that he doesn't need the AC switch on in the winter unless he needs to recirculate the air or help with defrosting the windows. I also think the AGM battery is charging faster and handling the cold weather better (or so i read they did).
Been over a week with zero issues, so I am calling this "good enough" for now. Thanks for the help.