Cm870 low oil pressure

[berrytrucking94]

Have a 2006 cm870 w/ 647,xxx miles. It’s been showing a steady 5psi lower than average on the gauge, having trouble figuring it out. Truck seems to be running with a little less power too

At idle it’s about 10-12 psi, going down the road it never gets over 25-27psi. I run delo w/ sta lube in it and have for years. Pressure has always been good up until 6-8 weeks ago

-Changed the oil pressure sensor
-cut filter open to see if there were shavings from worn rods/mains; hardly any metal in it
-did an oil sample ~4,000 miles after changing and the sample showed minimal/normal wear
-updated oil pressure relief valve but no change

Any suggestions as far as what we should look into next? Could Oil pump be on it’s way out?