I had a problem with oil pressure loss at high RPM in a big block Chev. It didn't seem to matter what I did to try to remedy the situation, it would lose oil pressure around 5000. Different oil pans, raise and lower the pickup, different oil pumps. However, there was something which I had done to the oil  pumps which I did not consider as detrimental. I had always been shimming the pressure relief valve spring in an effort to maintain higher hot oil pressure. The last time I had the oil pan off, I decided to remove the shims, and just let it do it's thing on it's own. Well, problem solved, no more high speed oil pressure loss. Why? Well, I am not sure, but I think what may have been happening is the relief valve could not open far enough to let bypass oil back into the inlet and this caused cavitation in the oil pump. Just a guess, but it is fixed now. No more shimming oil pump relief valve springs for me.