Intermittent Oil Pressure Fluctuations/drops to zero - 2001 5.3 in a Z71

[jocko]

I have an odd problem, thought I would tap into the experience on this board. I normally live in the 67-72 world, but my dd is a 2001 Z71 with a 5.3 with 242k mi - I realize "it's about time", ha....

So, here is the observation:
85% of the time, the oil pressure reading is dead nuts normal. Just like it has been for its whole life.

15% of the time, the oil pressure registers significantly lower, approx. 15 psi, and at a stop in Drive (the lowest I should ever see), it drops towards zero psi and triggers the oil pressure warning on the bright yellow message center.

Then, next time I drive it: Normal.

Maddening, eh?

Anyway, my research thus far leads me to believe it's probably some muck/blockage in the little metal screen in the passage that leads to the oil pressure sender. Have read of lots of instances of this being clogged and causing a false reading. But, I had one of the 15% occurrences today and noted that even if I rev'ed the motor, the max psi I'd see was about 20 (no load). It would very likely be fine if I drove it (which I've had to do thus far) with a load on the engine in drive - experience would lead me to believe this anyway. It SEEMS that if the pump were "going" bad, it wouldn't be "good" the next day, it would just get worse. But it would also seem that the likelihood of a clogged screen or sump pickup getting clogged and then getting better, over and over, is a stretch also.. HOWEVER, lately, the 15% is rapidly becoming 30% of the time - so I have a few questions:

1) Can the oil pump in an 01 5.3 "gracefully" degrade? In other words - can it have lower oil pressure one day and normal the next? My experience with older mech pumps is that they go from working to not working and that's it. Aside from a clogged screen in the old style pickups, it was a 1 or a 0, workie/no workie - so am curious to hear who's lost a pump and the symptoms you may recall leading up to it.

2) Is the screen the likely culprit? Has anyone had the sump screen clog?

3) If it IS the little screen before the oil pressure sender that is clogged - does a clog there inhibit oil flow throughout the engine or does it only inhibit oil flow to the sender? (I assume the latter - but this has been a burning question I've had - and may directly affect whether or not I harm my engine when these symptoms pop up)

4) Any other ideas as to what these indications could mean are welcome.

I've been milking this problem because it's been self-healing thus far. Time to address, and no time to experiment in a piecemeal fashion. If it's going down for maint, gotta get it solved (sound familiar)? Ha.