[littlehopper]

Along with what was mentioned, here are a few more common issues.
There is a screen under the oil pressure switch that clogs. The engine will still have oil pressure, but the sensor cannot read it.
Also, check the oil right after shutdown to see if it is aerated/frothy. Two things may cause this. First, at your miles/age, the oil pickup seal may have hardened and does not seal well. This allows oil pump to draw air past the seal. Secondly, there is an updated shield for the DOD relief valve in oil pan as GM found the oil spraying into sump aerates oil.
GM states to install this shield any time you do the lifters and have no history of it having been done.

Also, number 2 cam bearing is known to spin causing loss of oil pressure.

I would bet the loss of oil pressure is the screen under filter and noise at least one collapsed lifter. Small chance problem may be caused by the VLOM which controls oil flow to DOD lifters.

If replacing lifters, be sure to inspect cam lobes for damage/wear and valve train components for related failed cylinder.