John, I am running about the same setup and my
oil pressure with 10W-40 is now around the 60 mark. When I first started it up it was only around 45-50. I was using dual Fram filters and after reading some bad things about them changed them out to some Bausch filters. I could not beleive that the filters made that much difference. You might have a cloged or bad
oil filter that is keeping your presure down. Just a thought since it was at about 60 and went down that much!