[Only Toyota for me]

I run 60 psi all the way around towing our 8k lb fiver with 1250 pin weight.

This is PLENTY of air pressure, and there is no need to go higher unless you're overweighing the tire itself. You'd have to have over 7000 lbs on the rear to do that. At least i think an E rated tire is rated at 3500 lbs at 80 psi cold; or there abouts.

Now my C rated mud tire ( or 6 ply ) gets 50 psi all around when towing. This is max pressure for this tire, but it is only a 6 ply which is rated around 2500 or so.

Empty i run 40 front and 33 rear; either tire this is what i run. Got a set of 10-ply goodyear's for summer use.