You had no comment about my suggestion that you may have a venture effect where you are mounting your guage????????????????
Have you checked crankcase pressure/vacume for the possible effects of pressure differential causing the lower reading at the 4k?
And about your comments about the water temp thermostat--------if you (and others) weren't removing so much engine temp from the unnecessary
oil cooler, the H2O wouldn't be so wacko--------
We have been running some engines with dry sumps and crankcase vaccume pumps pulling so much crankcase pressure out that the
oil feed pressure goes to less than 5 psi because of the differential ---------
Why haven't you changed the bearings while you had the pan off----------proper bearing clearances is number ONE item in any list chasing
oil pressure problems----------