Out of interest, have you ever measured your hub temps?
I kept an infra red thermometer in my mog and checked the hub temps at each stop when driving long distance.
Tip - measure on inside of portal - temperature on the outside of the hub gives a less accurate temp reading as it is affected more by brake temps.
On hot summer days (35-40 degrees) my hubs would typically be 40-50 deg C (front) and 60-70 deg C (rear) after a few hours on the highway. I used GL5 oil in my hubs and never had issues with the portal hubs.
Braking has a fairly big influence on hub temps, so if you're driving down mountain passes, expect hotter hub temps than the above. Incorrectly adjusted brakes that drag can also result in increased hub temperatures.