Sorry I never updated this, just got preoccupied with other stuff and it completely slipped my mind.
I put the new battery in first. I couldn't see any sort of date stamp on it, but we get batteries from the Interstate truck delivered at work, so I at least know it hasn't sat on our shelf for very long. With just the battery installed, the truck once again fired up like normal, but it did still have the volt needle twitch and overcorrecting that happened when bottoming/topping out the windows.
I put the new ridiculously expensive Carquest VR on, which looked exactly like the cheap-ass one I got from Autozone(right down to the serial # stamped in the same place in the same font), and the needle sweep has almost stopped completely. It's still there, but it's so slight I figure it's good.
However, the whole reason I started this, the pyro, still hasn't been fixed. I'm going to have to talk to Westach I and see what their opinion of it is. I am using the same EGT probe and wires that I had wired into my previous pyro gauge, but it was wiped out when the Alternator went what?.
:EDIT: I've been sniffing around and found These. I'm going to get one to throw inline of my factory radio and aftermarket gauges.