Dd15 first fire after inframe concern...

Hello all.
Looking some experianced advice from wrenker:
I just finish my motor inhouse inframe dd15, new liner, new piston, new connecting rod, new main rod bearing ofcourse, new oil pump and oil suction module, new oil pressure sensor, new injector, new camshaft, cam gear, etc...
Late last9 I designed to do first fire after priming oil from 0 to full of level at oil module, priming fuel at low pressure fuel pump.
Everything look good and sound smoothly at the 5th cranking, however i noticed my oil pressure at the first start is at 66 psi instead of 75psi. I expect it gonna be 75psi on oil pressure at cold start. After 2 time short idle on low and hight, I designed to shut em off and dig into the job to see if anything happend but i cound not found anything yet to this point.
Does anybody have any experienced about this issue? I hope nothing to do with the crankshaft but upper cam housing causing this due bearing worn out. I am going to replace those cam housing/ rockers for today and fire again in the afternoon.
Any input i really appreciated...