To close the loop on this: I checked the dipstick after running. It did not show any oil splash above the bottom section that sits in the pan. This told me oil was not moving around the way it normally does. So I used the LS/weed sprayer method (YouTube) to pump oil into the side of the block after removing the galley plug on the left front of the motor. Then, when I went to start it, the truck didn't turn over because the 6 year old battery had finally died.
Upon install of the new battery, the oil pressure gauge jumped to 80 PSI before I even started it. Then, it crashed to 0. Once I started it, it remained on 0. However, pulling the dipstick showed oil splash up higher at the normal levels. That told me the pump was primed and pumping. I then took out the oil pressure sensor and replaced it. The screen was spotless. Now I have oil pressure at the gauge.
Not sure I understand it all. Definitely seems like there were two issues: pump prime and then the sensor failure. Throw in the dying battery and I don't know why. But that's what appears to have fixed it all.