I have a 1995 F-150 which was having low oil pressure. Changed the oil sending unit, oil pump, cleaned the screen and added a manual guage. Great oil pressure when it first starts running and then after while one of the lifters starts pinging. Turned it off and listened and you hear the oil SLOWLY dripping back into the pan. Someone suggested thgat the oil port holes are plugged and recommended taking it to a dealer and having the engine flushed with a Bilstein pump. Will this cure the problem?

 

I have read about the oil drain holes in the heads or the lifter valley getting clogged causing the oil not to drain back.. Did the dipstick show no oil while it was draining back?
Maybe you will luck out and it will be the holes in the heads. Good luck.