The oil pressure gauges in our trucks are notoriously inaccurate. This can be due to the sending unit, the gauge, or corrosion in the wires in between. In my experience, the oil level you describe has never caused the oil pressure to drop. I know for sure that when you get down below 2 quarts in the system, the pressure will definitely be affected (trust me on that one).
It's been a while since I've thought about it, but I believe the sending unit is on the passenger side of the block just ahead of the distributor shaft. You might have some success with simply cleaning the electrical connection.
-88 MJ; 4.0L, ex-2wd, TJ ax15/231, 78 Ford D44 w/spool, 9" w/posi, 33" trXus MTs, custom roll-bar/bumpers/etc.
Also an 86 MJ Metric ton and 2 '90 MJs
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