A friend called yesterday and asked me about this problem. Anyone have any ideas? Dodge ram truck with a 5.9. Oil pressure drops to about 5psi after it runs for 20-30min. Shut it off and start it up and it is right back to 30ish at idle, then after 20-30 min eases back down to 4-5psi. They had put a new sending unit in it and also changed the oil and filter. I told them to put a cheap oil pressure gauge on it to confirm the idiot light was working correctly and it was.It does the same thing (roughly) if it is the first start in the morning or if the engine is warmed up. They said it runs smooth and quiet.