Seems a little high too me. Firestone recommends 5-10psi empty. My 5er has around 2500# pin weight and I run 45-50psi loaded.
I determined this by measuring the height of the rear bumper unloaded, then hook up trailer, lift landing gear then inflate bags up to the same measurement. On my 5er, it is anywhere between 45-50psi depending on how I loaded the the inside of the Toy Hauler.
Also, I was told by Firestone that since I was not using an onboard compressor and in-cab filler control, that I should T the two lines to one schraeder fill valve so both bags are equal. This was recommended for a 5er but I was also told that if I was haulin an in-bed camper, to have separate fill valves and to inflate both bags to the same pressure. My fill valve is located in the rear bumper beside my license plate.
Their theory is that a top heavy camper when cornering will not transfer air from one bag to the other if hooked together. This is ok on a 5er since the weight is at the bed level and there is very little if any air transfer from bag to bag.
My truck corners on the highway close to the same with or without the trailer behind me and I have no sway or leaning happening.