So I have low Oil Pressure, now what?

[NCboatrx]

To the original poster.
Kubota's spec on this engine is 24 to 64 PSI at rated speed.
14 PSI at 900 RPM idle with a 7 PSI limit.
I suggest that you use SAE 30 Rotella (non synthetic) and without any added additives and you will most likely have no issues.

[Ding Duck]

I found this in the service manual for a Nanni MA245HE - 375HE Engines.
LUBRICATING SYSTEM
Engine Oil Pressure
At Idle Speed More than 49 kPa
0.5 kgf/cm 2
7 psi
At Rated Speed 196 to 441 kPa
2.0 to 4.5 kgf/cm 2
28 to 64 psi
This would tend to line up with the rule of thumb of 10PSI / 1000 RPM.
Would also explain why Oil Press alarm is set to about 5 PSI.
So if the OP Engine is running at 45 PSI when hot, then it's about mid range and would seem to be OK. Perhaps an inaccuracy in the guage ?