Headlight/Electrical Issues

[Big69C20 Toy]

Hey all, on my recent trip out to MI from Cali, i ran into some electrical troubles.

In Eastern Colorado my low beams decided to go out, as they had done before intermittenly in years past. So i just dealt and drove on with the hi beams (sorry to all i passed with 130W blue xenons).

Anyways the truck drove on and was fine but i'd notice at times that my voltmeter would be seemingly dragged down, then kick back up to 14.7 or whatnot after a bit. That is until western michigan, my volts kept dropping and dropping until i didnt have enough juice to accurately fire my ignition system (man that sounded like heck)

Pulled off the highway and i had juice but not enough to fire up the truck, got a jump and proceeded to get a new Bus fuse for the headlights thinking that may be the problem, not so. I still had no low beams and my highs would keep draining the system, heck i dunno if it was them or the running lights or what exactly

So my question is what should i check out on this thing? It has a stock style alternator that is i dunno how old and with that 572 under there i thought the thing might be overheating or something too.Perhaps my voltage regulator (dunno what it even looks like) Driving the trucks with no lights has proven fine but i'm unsure.

Some direction/advice would be great. Thanks fellas.
Greg