If they're little E rated tires like stock size on duallys the door sticker will say 80 psi.
Capriracer is not correct that you should always follow what the door sticker says.
There are multitudes of tire, wheel and load combinations that make the door sticker completely useless.
Now the newer trucks with Tpms make the situation even worse because the max psi is typically programmed into the ECM which does not allow for airing the tires to match conditions or load without getting an idiot light on the dash.
As well over or under inflated tires can and will wear substantially faster depending on the conditions they are subject to.
In short if you have E tires on the back of your dually good for around 3klb each then air them accordingly to the load. Running empty I wouldn't have more than about 30-35 per tire. Loaded pressure depends on the weight.
Don't use the door stickers to tell you he right way to air your tires, learn what is right for he conditions you're using them under.
I was frustrated enough on my newer F250 that I found a dealer who'd reprogram the tpms trigger pressures and had them all set to 30 psi. Now I can air down on ice or sand or air up for heavy loads without affecting the tpms sensors.
Your truck is old enough to not have to mess with all that.
