Aug. 31, 2019 update. The Yukon is still running fine. Mrs. Cusser states that the warning occasionally shows up on start up on cooler mornings.
I've driven it about 2 miles personally since then.
Two months ago the mechanic replaced the blower fan and blower resistor to fix the AC fan operation. He wasn't concerned about the oil pressure low warning, and said not worth it to replace the oil pressure sending unit.