Very Low Oil Pressure in New Engine

I have a rule - If oil pressure changes drastically after breaking it in, pull it and inspect everything. You will catch problems in most cases before they really get expensive and all it costs is time, gaskets, and oil/filter. The rods - if they are .0015" they were tight. If the side clearance was not checked they may have been tight. If the thrust clearance has changed at all, tear the lower end apart very carfeully and inpsect.
Some hints:
Always always always always take the new oil pumps apart, pull the cotter pin, and remove the relief valve so you can clean and blow out the passages.
Always always always keep the notebook where you can get it quickly.
Always always make sure the bores and oil galleys are spotless clean when you're washing the block before final assembly.
Always verify by backlighting and looking down each passage that the cam bearings are positioned to allow for full oil to the top end.
Always triple check the oil galley plugs during assembly - I place a check mark in my assembly notes to verify I did it - Once after the cam breaings are in, once after the crank/pistons are in, and once before bolting on the tin and intake. You might be surprised how often you find one missing somewhere just before the intake goes on...lol