Oil pressure low in 427 C/O

[Eljaro]

My 427 C/O got new rod, main and camshaft bearings recently, with the crankshaft reground also. All done by an experienced machine shop. The engine got a new camshaft, lifters and new Dove rocker shafts. An oil restrictor to the rocker shafts has been installed in the Dove F5 aluminum head also. It has a remote oil filter with a FRAM HP1 oil filter, an oil cooler and oil thermostat in between. The oil pressure pickup measures the pressure AFTER the oil filter and oil cooler, actually the pressure going into the engine.
The engine runs fine. At first I used 15-40W Castrol oil, and the pressure was 15psi at idle(800rpm) and 50psi above 2000rpm. I wanted to improve that , changed oil to Shell 15-50W but now I have 10psi at idle hot and 45psi above 2000rpm,
It has a Melling MV57HV high volume oil pump, which is almost new,and a bafled Canton Oil pan. 8 liters of oil total
Outside air temp here is around 95ºF.
I am worried about the low oil pressure, especially at idle , and do not want to rev up above 4000rpm until I am sure 45psi is enough for that.
I have read of some 427 owners reading oil pressures of 30psi at idle and up to 80psi at 3000rpm , and all that with 30W oil !
What can be wrong with my engine? Is my oil pump no good? Are some of the 80psi guys reading oil pressure before the oil filter? Is my oil gauge faulty?
Need help from all of you!