The minimum and maximum air pressure will depend on what type of air bag kit you have installed on your pickup truck. If you are hauling a 5th wheel trailer, you most likely have a Firestone Ride-Rite or Air Lift LoadLifter 5000 air bag kit. The minimum air pressure is 5 psi and the maximum is 100 psi.
What air pressure you should run will depend on your trucks suspension and the tongue weight of your trailer. It will vary from truck to truck and there is no recommend air pressure for a fithwheel trailer. We typically start out at 40-50 psi and inflate or deflate the air bags from there to get the ride that you prefer. After adjusting the pressure a few times you should be able to tell where you need to be.