Back in Aug. of '93 GM issued a service bulletin: 93-286-6A I can print it out and post it if anybody wants it, but it can be looked up on the internet. It was about the oil pressure switch failure problem. There was a new oil pressure switch designed to fix it with heavier contacts for the LP. Part no. 10243574.
My OPS failed about 10 yrs. ago and I replaced it with the updated part and have had no problems since. The LP mod. mentioned here is a good way to go, I'm just mentioning this as the newer model of the OPS has worked fine for me for those 10 yrs.
'93 C2500 280,000 m.
60k on new AMG mil. surplus engine
Turbo with name that starts with A.
Straight pipe exh. (but it ain't that loud).
Boost, EGT, Glowshift intercooler in/out temp. 3 guage pod.
Rebuilt complete susp. with polyurethane bushings. (Bad idea).
20k on GM 4L80E rebuilt trans.
Dual thermostat/Duramax fan/high flow water pump.