All a heavy weight oil does is increase wear at startup. :eyepoppin
It also robs you of some horsepower as does a high pressure or high volume pump. 59PSI sounds high even for a high pressure oil pump.
Is the gauge mechanical or electrical? If it's electrical, you may have used sealant on the threads. That might be insulating the sending unit from ground which is the block via the threads on the sending unit. That might result in a higher reading than actual. :?: