ok,it holds about 30lbs of oil pressure until you run it hard or it gets good and hot then at idle it'll drop to maybe 10lbs.If you keep the revs up the pressure stays but i know 350 a usually run about 60lbs pressure.Ok i know this wasn't smart but i got aggravated and rev the motor to the moon in neutral,like 5k and noticed something.The higher you rev it the less loud the tapping,but i did have light gray smake coming out of one side of exhaust.At 5k rpm there was no knocking or tapping just the sound and fury of a dualed 5.7 with glass packs except for the smoke.,I also changed the oil and via speaker magnet found a few metal shavings,the oil was really bad.Please anyone with any ideas are welcome and are thanked very much,It just seems like if were a rod it would have went through the block a 5k rpm with no load on the engine but i could be wrong.Help me please,thank ya'll.

morbid; Check the oil pressure with a manual type guage by removing the oil pressure sending unit and inserting a guage, there. If you continue to rev it to 5K unladen, this becomes moot.
Loren
SW WA

 

I HAVE THE SAME TRUCK AND HAD THE SAME PROBLEM CHECK THE PUSH RODS UNDER THE VALVE COVERS AND WHEN YOU CHANGE THE OIL IT MAY BE BLACK IN NO TIME SO CHANGE IT AGAIN .THE OIL PRESSURE IS NORMAL