Try replacing the Oil filters, be sure to clean the surfaces carefully and not over tighten.
From the sound of what you were saying about the leak, It really started "after" the oil change or within a short
time period. Maybe you have a bad filter...
This would also explain a lower oil pressure reading. And for my next trick... Do you have 1 or 2 oil filters?
If you have 2 then one is probably a hight flow and the other is a low flow with bypass.
If they put the wrong one or both on the bus or got the postions reversed it could explain
the pressure problem and possibly the cooling issue.
The High flow is in the Oil cooler circuit, The low flow is usually routed back into the engine at some point.
If someone put a low flow on the postion for the HIGH flow, It would restrict flow to the oil cooler and make
the engine run hotter.
Now.. If your engine has 195 degree thermostats. It will run up there around 200 but not usually more than 210.
If you change to 180 degree they will only open sooner and not affect the coolant flow.
Are you sure that your temp gauge is working correctly?
But, If someone removed the thermostats, The engine could run hot all the time because that huge water pump
sends so much water through the radiator that it doesn't have time to get rid of the excess heat. ( Dwell Time ).
Just some ideas, Most lifted from previous conversations about cooling issues on different engines.