oil pressure gone funky

[little girl]

has anyone experienced this problem?

i have: '87 GMC K10, 350 Jasper crate engine (30K mi on engine & gagues), mechanical AutoPro oil pres gague, mechanical oil pump, truck only gets 'super' fuel, oil is religiously changed every 3K (mobile 1 & pennzoil filters)

problem: when sufficiently warm (190 deg), oil pressure drops when throttle applied. The faster I accelerate, the faster oil press drops - if I punch it, I have 0 oil pres until I release the throttle. When throttle is released (no matter how fast I'm going) the oil pres slowly climbs back up. Check Engine lights up for the duration of the period of 0 pres.

background: just changed oil 5 days ago, started the day i changed the oil. Oil is still full and clean, no gas smell, etc, no leaks. Just changed oil filter today to see if faulty check valve - no dice, problem still exists.

Has anyone ever experienced something like this? me & my mech are baffled, just doesnt make sense - trying to see if I can dig up some clues before I rip the oil pump out and call Jasper. Thank you gentlemen!

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many thanks guys!