Bah, head gasket.
I noticed the coolant beginning to burn rapidly. Nothing in the oil, no oil in the coolant. However, I'm attributing the fluxuating temps to steam pockets in the cooling system, caused by emissions leaking through the head gasket. The old gasket looked pretty bad.
That, and when I gassed the engine, the overflow would bubble with emissions. So, the head is off, the headaches have begun, but hopefully this will remedy the issue.