I once had an issue with
oil pressure dropping with increased rpm's. I had just installed a new timing chain along with a new HV
oil pump and pick-up tube in a 289 in my '66 Shelby GT350. When I started the engine, the
oil pressure would DROP when the engine revved. The cause turned out to be a hairline crack in the (new!) oil pick-up tube that I had just bought - it was sucking air when the engine was revved up.
Jeff