Just run the factory recommended pressure for the stock sized tires and you'll be fine.
I have Ridge Grapplers on my SUV and they are great, but I probably would not have put them on a tow rig. Mine are 37x12.50R17s on a Chevy Blazer that I use for some pretty serious off road use. My truck has the Terra Grapplers. I would have wanted more siping for a tow rig just due to the possibility of bad weather. On my Blazer (5500 pounds or so), I run them at 25-30 psi on the road and anywhere from 8-14 off road.
It's okay to set pressures based on loading for a single vehicle, but once you get into a combination vehicle, the dynamics of weight shift come into play, and you're going to see that you have more control with a higher tire pressure.
I would probably run something like 60 and 80 psi. I actually run my front tires at 70-75 psi when loaded and rears at 80 always, but I'm also loaded closer to GVWR. Empty pressures are 50 and 40, if I recall correctly.
There's nothing wrong with lower tires pressures when empty, but especially in the rear, more pressure is going to be safer and you'll have more control when loaded.
If you notice more center wear, run lower pressure, but I doubt you will, especially if your rims are wide enough for your tires. I run a 285/70R17 on my Ram on 8" wheels and they have been wearing just fine for years.
I understand the argument about tread squirm, but I'm also not sure the Ridge Grappler is aggressive enough for it to come into play. The Ridge Grapplers don't have the void ratio like a mud tire.
