87 F250 6.9 Oil Pressure

I just purchased a 1987 F250 6.9. My first diesel. The oil pressure gauge is bouncing between low end and middle of normal range. I have changed air filter/ and oil/oil filter(Motorcraft) using Rotella 15w-40. The intake and bolt to air cleaner were not covered in oil, but we plan to address CDR valve next. I have read other post which talk about poor readings for stock gauges. Any suggestions on a good set up and/ or repairs to insure I am getting good readings.:ford:

Thanks