Mr Magoo:
Dennis's idea of the 10-30 is valid. Yes the HV pump takes more "effort/torque" to turn and therefore loads the gear more heavily, especially if you are using 20-50
oil. Unless you are running bearing clearances that are looser than standard or a remote filter/cooler the pump will be in "bypass" constantly and will beat the
oil and put more heat into it. That may explain your
oil temps.
Rick