Continued Oil Pressure problems

I have an 02 X-star with 310 Predator. 440 hours. I had a warning alarm go off the other day and noticed the oil pressure seemed lower than normal, 10psi or a little below at idle. At 3K rpm, it was fine right around 40psi.

Tonight I put the boat in the water. Started it up. Oil pressure right around 40PSI at idle. Drive around for a few minutes and get boat up to temp and pressure was still right around 40psi for idle and at 3K RPM. Pull riders for about an hour and oil pressure still right around 40 both at idle and at 3K RPM. A little while later, the warning alarm goes off while I am at idle. I look down and the oil pressure is just below 10psi? Now what would cause the oil pressure to be at 40psi for the first hour while at idle or at speed, then half way through the night, it drops to 10psi at idle but still 40PSI at 3K RPM? I'm confused. I'm about 10 hours short of needing an oil change, but will start there and see if that any difference. Any other ideas at what may be causing this? Oil level is good and the oil looks good. Engine temp is fine too. No clatter from the engine and no leaking oil that I can see anywhere. Help.

I would run a manual oil pressure guage and see what it says. My guess is a bad oil pressure sending unit or faulty guage or possibly a ground issue as most guages work through ground.