How often do you check your Truck's tire pressure?

My truck has TPMS so I can see the pressure each time I start the truck. With older trucks I would check the pressure once a month unless I found a tire that was more than 5 PSI low in which case I would monitor it weekly until I was sure there was not a slow leak.

I am most concerned about the rear tires as their maximum load rating is based on having 80 PSI of air inside.