@My2ndgen678, I have no experience with heavy-duty trucks, but it seems your truck is set up to utilize every bit of load-carrying capacity of those rear OEM LT245/75R16 tires called for on the placard (E-rated tires carry a maximum pressure of 80 psi). At bare minimum, I would think if you are totally unloaded, you can easily air both front and rear to 65 psi and be completely fine, since the front will always be heavier than the rear when the truck is unloaded.
If you're willing to be a little riskier, I would hazard a guess that 55 psi front and rear would also be fine when completely unloaded, but then you're getting into speculation territory, and as I said, I have no experience with HD truck and major towing. See if some of the other HD truck guys here can weigh in on that.
Also, keep in mind the above pressures I'm discussing are assuming you have the OEM tire size. Because you have a different size, you can use
this handy calculator to determine what the tire pressure should be in the alternative size given the input parameters it asks for, to maintain the same load-carrying capacity. Experiment with it a little bit to get a better sense of the pressure equivalencies.
Also make sure you read though all the threads on this topic on the forum. I'm sure there are many. It just take a while. Good luck!