Low Oil Pressure 2009 Ford E450 RV Class C

I am currently experiencing low oil pressure in my 2009 Ford E450 RV Class C. At idle its 25-28psi. At 2000-3000 RPM (no load) the psi increases to 50-55 psi then drops back down to 25-28.
Here’s the back story. We were on our way from the Atlanta Ga. area to Dayton Fl. and the oil light came on and the gauge dropped to zero. We had it towed to a repair shop where they diagnosed it to be the oil pump.
The oil pump along with timing kit was replaced. During the repair the the valve covers were removed to get access and found that the internal covers for the PCV were falling off onto the rockers. One side had the plastic worn material sitting on the head while the other was still clean. Prior to picking up the RV an aftermarket manual gauge was put on for test purposes (then removed afterwards) where is was reading 50-55psi sitting for a bit and test drive.
We picked up the RV and got on the FWY and within a few miles lost PSI again. The oil light began to flicker then went out and once it did the gauge went to zero. We turned the engine off and waited a few minutes, then turned it back on. The light stayed off and the gauge was reading just past the halfway point towards HIGH pressure. We limped it back to the shop, re-installed the manual gauge along with the sending unit so we could read both.

We called a Ford dealer and they said it could be the main bearings or the oil pump seal was damaged. We have searched and asked the dealer what the oil pressure should be but we were not able to get any real answer obviously because it depends on age, wear, oil, temp, etc.
Our next plan of attack is to replace the aftermarket gauge and retest. It seems that most testing and work requires the engine to be pulled including the oil pan to check the pickup tube.

Any help on what to look for would be greatly appreciated as I am really not wanting to pull the motor and spend lots of $$$.