Yes your right, but I would still use the pressure setting in the manual. Not the pressure shown on the tire it self. Then stop by a tire shop and they should be able to give you a more accurate pressure setting based on your vehicle weight.
I owned a 97 TJ and also ran 30" tires, but I don't remember what pressure I kept, my tires at. I really liked my TJ in a lot of ways better than the JK. To me it was a lot simpler machine and not bogged down with all this computer control BS. I guess I'm just old school. As already stated in previous post airing down when your off-road is going to make a big difference in your ride quality. Good luck and enjoy your Jeep.