If you're losing
oil pressure with rpm, it's most likely that you're running out of
oil in the pan.
Either you just don't have enough
oil in the pan, or your pickup clearance is such that it's either being uncovered or too close to the pan to flow enough oil.
Could be some other causes too....a galley plug missing somewhere which causes an internal bleed, too much oil going to the top end, etc.
It's not uncommon to lose a few psi at the top end, but if you're just getting into the gas above cruise rpm and you're losing pressure, I would lean towards my previous thoughts.