Just check or replace in the order of simplest to hardest. Probably:
1) Filter
2) guage/send.
3) Pull valve covers
4) drop pan
Cut open the just replaced oil filter too
Myself, I would
1. Put a drill motor on the oil pump drive. Take a reading. The advantage to doing so is you now have a constant RPM on the pump to take and compare readings. In addition, if there is a problem no further damage is being done by starting the motor.
A Corded electric drill would be preferred as you are removing the variable of a cordless drills battery. Yes I still have 3 or so LOL
2. Then install a new or known good mechanical gauge and repeat.
3. Compare the two.
4.Only other variable is the oils which you could change again if desired but a pricey option
5. Pulling the valve covers is easier that the pan but if # 4 doesn't revive the pressure see #6. If you do pull the covers make sure the ends of the rocker shafts are not leaking (longshot)
6. I going to agree with a few others and guess that the relief valve in the oil pump is hung slightly open or the pickup tube developed and issue.
The good new is no metal in the filter
keep us posted
