Got it....
It was the positive cable.
I had already cleaned the cable ends and terminals the last time it happened and everything worked fine for 2 weeks, until today. I tested the battery voltage and the voltage at the distribution block and had 12.7 volts in both spots. Still, I took it to O'rileys and it did test good. So I decided to check the cable ends again amd noticed the positive end had been replaced and the wires weren't corroded, but dirty and and a little greasy. So a bit of disassembly, cleaning, and reassembling, and she fired right up.