As this issue comes up a lot, I can't seem to find my specific situation.
My 2009 chevy 3500hd with the 6.0 had low oil pressure. Around 35 or so I figured it was the pump. Did that and the o ring and nothing. (Did it once before on another 6.0)
My mechanic replaced cam phaser, timing chain(had other issues), oil pump, some other stuff in that region, new valve springs, new heads and new lifters.
Engine was also generating a lot of heat although wasn't overheating. Replace the oil pressure sensor behind the intake too. Was within spec while driving (20psi) or idle (6 or 7psi I think), but now the oil pressure light is going off and dinging. Engine runs perfect, idles perfect, with no lifter noise.
Is it possible its the cam bearings? We are running 10w 40 oil and Lucas to thicken it up but still has no effect.
Want some opinions before diving in further.