When it comes to towing with passenger rated tires, I would definitely tow with the maximum PSI listed on the sidewalls.
rbpru makes a good point as well and makes good sense. ;)
I have "LT" tires on our truck and highly recommend "LT" tires as well. However, I have no reason to inflate them at or even near the maximum PSI listed on the sidewalls. And I have never had a towing performance due to the tire pressure with which I run. :)
Now for our "ST" TT tires, I always fill them to the maximum air pressure listed on the sidewalls.