The oil pressure sending unit that supplies signal for the 0--60 psi gauge on the dashboard of the TBI-era V-8 engines is a known "common-failure" part.
I had a spraying-oil type of failure which put the final nail in the coffin of my sending unit, which has been reading considerably higher pressure than it had any right to for a couple of years now. (The previous sending unit was replaced because it indicated too-
low oil pressure)
My usual supplier is NAPA; and the sending unit which had just failed was a NAPA purchase back in about 2003 or so. When I tried to buy another replacement oil sending unit at NAPA, I discovered that the part they're currently selling does not fit my '88 K1500 5.7L. The diameter of the sending unit is so huge that the heat-shield has to be forced into place; but even worse is that the sender hits the engine block before it can be screwed-into the pipe-and-80-degree elbow arrangement that GM provides.
The original sender and heat-shield on left, and the too-large sender and NAPA part-numbered box on right:
Original sender and OEM eighty-degree pipe/elbow on left, too-large sender and 90-degree elbow/pipe that I tried to make work. (Failure--if it's far enough out from the block, it runs into the exhaust.)
Far as I can tell,
NAPA (p/n OP6649) and O'Reiley's both catalog the wrong part number, and they don't fit. CarQuest catalogs a different part number (p/n 57013), and those fit reasonably well. I returned the NAPA sending unit, and installed the CarQuest sending unit.
(Edited: See post #3 for current part numbers)