What could be causing my Thermostat "R" wire to only be 8 VAC?
I had a furnace guy come in the morning. He saw the furnace and said "Oh my god!"

After two hours he decided he couldn't figure it out and they sent another guy later that day.

They finally figured it out.

Since a guy who works with furnaces for a living couldn't figure it out after two hours I think I never had a chance to begin with.

So in the end, the answer was:

Call a pro.