What PSI on Truck tires to pull my RV?

[justRich]

Run the tire pressure at the maximum for which the tire is rated on the truck.
The trailer, I don't know.

I run my TC (truck camper) at 80 psi and have for years.  Current TC weight is 14,000 pounds and towing a 5,500 tow vehicle.
What you may notice at high vs low tire pressures is vehicle handling.  

Remember that, tire pressure recommendations are good even for tires that are near completely worn out.  
There is a wide safety margin built in.

The very common Dana 80 axle, as used on many 350/3500 products, direct from the axle manufacturer (not Ford, Dodge, GM, etc) is for 11,500 pounds.
Vehicle manufacturers de-rate the axle rating (GAWR) to conform more to the tire maximum load capacity.
Thus, you will find that an vehicle's tag will rate the axle load to within a few hundred pounds of the tire load capacities. 

I've made the Dana Axle Spec Sheet available here: https://www.eaglecapowners.com/owners/showthread.php?tid=224

 

[TireHobby]

11 hours ago, Rich&Sylvia said:

Run the tire pressure at the maximum for which the tire is rated on the truck.
The trailer, I don't know.

I run my TC (truck camper) at 80 psi and have for years.  Current TC weight is 14,000 pounds and towing a 5,500 tow vehicle.
What you may notice at high vs low tire pressures is vehicle handling.  

Remember that, tire pressure recommendations are good even for tires that are near completely worn out.  
There is a wide safety margin built in.

The very common Dana 80 axle, as used on many 350/3500 products, direct from the axle manufacturer (not Ford, Dodge, GM, etc) is for 11,500 pounds.
Vehicle manufacturers de-rate the axle rating (GAWR) to conform more to the tire maximum load capacity.
Thus, you will find that an vehicle's tag will rate the axle load to within a few hundred pounds of the tire load capacities. 

I've made the Dana Axle Spec Sheet available here: https://www.eaglecapowners.com/owners/showthread.php?tid=224

 

Vehicle manufacturers sets axle GAWR to comply with vehicle specifications needed to comply with vehicle certifications. Whatever axle manufacturer's specifications exceed the vehicle GAWRs is considered reserve load capacity. Tire load capacity is based on maximum GAWR and the regulations that stipulate tire load capacity reserves for automotive vehicles.

NHTSA does not knowingly allow deviations from vehicle certifications. Recalls for inaccurate vehicle labeling can be very expensive for vehicle manufacturers, yet we see them almost weekly because some vehicle manufacturers are lackadaisical about the process.