GFCI Showing Reverse Polarity
I determined it was a faulty gfci. I exchanged and reinstalled and it checked out correctly, reading "open ground". Then ran a ground wire from some conduit about 12" above the outlet. Everything checked out correctly with the testers. Voltage checked out correct H-N at 118V, N-G at 0V. And it tripped the gfci when I did H-G. 

When I returned the first one to ace hardware, the cashier said I was the second person that returned a gfci the same day for the same reason, so they must've gotten a bad batch that somehow had reverse polarity.