Matt,
I like your low voltage theory. Tough to prove if it's intermittent.
Clean up the larger current carrying connections on engine, alternator and
battery. Rework the connections at the ground clusters behind the fuse
box.
I actually added a few extra ground braids between engine/chassis and
alternator/engine. Gained about two volts (at the headlights).

Ken Lewis
http://neksiwel.20m.com/