You mean the truck tires? They are 80 psi front and back for towing. At least on Fords and I suspect the other brands are the same. On my Ford the tire low pressure alarm is set at 65 psi so you can't really air them down lower than 70 psi.
I have never run 80 in my front F250 E rated tires. They run, perform, and wear best at 65 psi for me.
By the way, you put out some bad skinny on the on board TPMS. I run my tires at around 60 psi or less when empty. That warning threshold is adjustable and i had the stealer set mine at 55. So now i can air down and the F250 feels like riding in a well lets say something a little less than a log wagon.