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I'm sure there is a diagnostic test for it. Have you checked the ICP voltage to see what the pump pressure output is? I know they are all three related, but you have to start somewhere.
there is in fact a way to do it. I would love to tell you the correct way but you failed to say what year the truck is and if its an o4 early or late build as ot does change things a little bit.
You can pull the ipr valve out and see if the screen is torn like something went threw it. if so I would suggest replace and retest.
on an 03 you would varifiy you have base oil presser then you would air test the system while active commanding the ipr to listen for a change in air flow. no change means bad ipr.
from there you would need to remove both oil supply lines from the heads and dead head the pump while watching icp. and see what max pressure is on the pump.