Sorry to hear your having trouble.
I guess we can assume that your many thousands of miles running in, would have got the engine hot enough to open the thermostat for the cooler?
If not and you have only just started leaning on it, could it be the first time the cooler has become operative.
I only suggest this as if it's never had oil in it, then when its filled would this have given a pressure drop?
I'm assuming you didn't add any more oil to the system, so would expect the oil level to have dropped a little.
If it were me, I would put the oil side of things back to stock.
Do a pressure check on cranking, then cold, and running, and see what you get.
I wouldn't have thought a minor overheat would effect the oil pressure, especially not in a negative way ie. Less pressure when running.
Seems never ending
Nb. I assume you haven't also got really long oil lines to the relocation, which will also cause a negative impact on the pressure of the system (once it's in full operation, thermostat fully open).