Oil Pressure

It is probably just worn out a bit. The bearings, crank, rod, cam are probably worn. Still good at speed. Napa filters are good units.
The pushrods and rockers also probably have some wear on them as well. If it is that bothersome, you can get HD rockers from MoPar along with new pushrods and lifters. If you get lifters, I would run some dino oil on them for a while before returning to sythn oil.

My 318 also has this high to low oil pressure drop just like yours. When I opened it up, I did the cam bearings. Slight improvment. Crank and rods bearings would have help alot, but it is still in a safe zone so I'm not worried.