Oil pressure issues.

I have asked this question before, but I am going to try again. I have a 540 big block Chev with an oil pressure issue. This is a bit of an ongoing problem, and I have received lots of information from various folks trying to help. Believe me, all the possible remedies they have offered, I have tried, checked and double checked. Now, the problem is a loss of oil pressure above 5000 rpm. No one else seems to have this problem, yet this is the second engine that I have had that has this issue.

I run a Moroso billet oil pump and I try to maintain 65 psi hot oil pressure, so the bypass is shimmed up. I run -12 lines to the oil filter. I run a Moroso oil pan with 8 qts capacity, although I run other oil pans, (larger and smaller, stock and non stock). I have run different oil pumps. I have checked the pickup to oil pan clearance, and varied it. I have varied the oil level up and down. The engine does not sit at a crazy angle or anything. This problem has never shown itself on a dyno, (but maybe the rpm is not held there long enough).

I THINK the pump is pumping the sump empty at high rpm. I also am considering going to a standard, stock, non high volume oil pump in an effort to correct this problem, or at great expense, change to dry sump. As I is right now, I cannot use full power, and frankly, I don't know what the solution is. Opinions?

Oil pressure issues.