low oil pressure

Hmmm. I am having the same problem - only I know that the engine is new/fresh and all the clearances are checked and rechecked. Everything is new. Has a new Melling HV oil pump, drive gear/shaft and pickup. I have checked the pressure with two different gauges - same result. I have come to the conclusion that it could be ; the oil pump relief, a filter pressure relief (2 different filters - going to try a wix gold next) or maybe perhaps the oil pickup is too close to the bottom of the pan????
This is really bugging me! The motor is ALL fresh, balanced, new +.040 KB pistons, scat rods, standard crankshaft, new comp cam, lifters, pushrods, etc. The block was thoroughly cleaned as was the crank.
Does anyone have ANY idea???

Flummoxed!
Cheech 14