I have replaced the sending unit and installed a tee and 1"oil pressure guage as well to cowitness the oil pressure. Oil pressure is excellent.

My oil pressure guage is erratic.

Sometimes the pressure is perfect and at other times it reads low.

 

My 91 gages in general are erratic. The Oil generally reads fine but has recently started reading high and then all of a sudden it will drop back to normal. (Not as nerve wracking as low pressure though) My temp gage also has a tendency to read high then within seconds will drop to the thermostat level.
I figure it may be in the connections but haven't done anything about it yet. Considering a reworked dash from Hawks (my tachometer is also pegged)