Can anyone explain this oil pump problem?????

[Longhorn Man]

OK, yesterday I lost all oil pressure in the caddy motor. ( http://67-72chevytrucks.com/vboard/s....php3?t=144642 ) I know it happened, I have a witness. (I was actually starting to wonder if I saw and heard what I had thought I saw and heard)
Well, I go out there today to grab some parts out of the box that I had bead blasted for a buddy of mine. I don't really know why I did it..but I hopped in and fired it up.
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40 psi of oil pressure.
I got a PM about a plunger that can get stuck, and I'll be looking for this tomorow (or thursday..when ever the parts get in) when i rebuild the pump.
Even so, it's still enough to make you crazy...or at least wonder if you are crazy.
40 PSI with thick sub freezing oil (10w30) isn't really much to brag about, but it is better than the 5 psi I was getting at 4000 RPM yesterday.