Isnt 15 psi a little low on idle for a newly build engine?(i know its still in the range,, but i get crazy if mine go below 25)
If i where you, id get a new mechanical oil pressure gauge, fresh "wix" oil filter or equivalent, simple things first.
With my 383, on initial cam break in, it would never go below 65 psi. hot or cold...
After the initial cam break-in i had a pressure about 45 psi, never below... A few miles later pressure got down to about 20-25 psi... :/(i know its still in the range)
I changed the carquest oil filter for a WIX(or equivalent) brand oil filter.. i also changed from 10w30 to 15w40.
Oil pressure was still a little low(in the 25-30psi range at idle), after a few miles(engine now has 84,5 miles) my pressure is stable at about 35 psi on a hot idle day and on cold start its always over 60(going about 80psi as rpm raise).
Maby those bearing just need some more break-in?, its strange the pressure lower as the rpm go over 4k.. That usually is a incorrect oil pick-up for the oil pan(pick-up too close/too far to bottom of pan). But you already taken care of tyhe pump/pickup so.
If you have the engine out.. id check the whole oiling system(oil gallery plug, pump shaft, oil filter adapter...etc). And am curious about the lifter/bore we all talk about the rotation asembly and bearings but not the upper part of the oiling system.. i know its non-sense, but i like to overdo things... :/ thats just me. Am posting so you can have a oil pressure comparison with another fresh 383 sbc.