I think 5 psi is too low.
Pontiac engines have main clearances from 0.0002" to 0.0020".
If a builder or machine shop is not familiar whith Pontiac they will go with the greater clearances of a small block chev or ford.
The machine shop I took my block to machined the mains for a 35 thou clearance even though I told him I wanted 20. I had him redo the mains to get the clearance I wanted. I now have 25 psi at a red light in hot weather and am not worried about a melt down.
Your builder may have machined the main and rod bearings for a larger clearance resulting in low oil pressure, or it may be a failure, lets hope for the former.