I found this chart that will tell you the weight rating at a given pressure for your tires.
For max pressure you should be using the rating printed on your tire and it sounds like you have “E” rated tire which is 80 psi. The rating on the door jam is only for “stock” tires. If you do have E rated tires you been under inflating your tires for asphalt/hard surfaces.
Choosing the correct tire pressure for your rig will depend on road condition, your weight and truck suspension. These are different to each rig.
I have a 2007 F250 carrying a Bunduvry camper a little heavier than your rig and the most I would air down is 35 psi.
TCA has several write up on some moderate off the highway trails you may find interesting.