Oil pressure dropping

[carco]

Hello to all during this hot stretch,
2009, T8, ISX550, 326000 miles, 14400 hours, empty weight 52K, loaded usually 65K to 90K often up to 130K but has been up to 167K, and once 232K.
Oil pressure has been dropping last 4-4500 miles 68mph, 1700rpm oil 39psi is now 33psi hot.
Hot idle oil psi now 16psi was always over 20psi. No power difference, no sound difference.
Was ready for oil change, 10 to 12K service intervals, so changed oil, made no difference. Changed oil sending unit, no difference.
So am I in trouble just over the next hill?? just keep an eye on the oil press?? tear down the engine, pull rocker cover chk cam, pull pan chk rods and mains??
Any words of wisdom?
Thank you.