It would be very unusual for a Mechanical problem to result in high oil px when the engine is hot, the oil you are using is top quality and has a very stable viscocity at high temps but is unlikely to be the cause of the high px indication.
I think that you should look at the indication system, if it is one of the electricly driven gauges it is likely to be the problem.
As stiknruda says you can adjust the PRV but this should only be done if you have a calibrated gauge rigged into the oil system DO NOT trust the cockpit indications as they may be the problem.