There was a thread on this last year (or so). I seem to recall that if you're running Light Truck tires (10 ply, rated up to 80 psi) like I am, you need to calculate or measure the appropriate pressure to use? Somebody had a chart from the Tire & Rim Association to calculate. There is also the chalk method, which displays tread contact with the pavement.
You dont want to just fill to max pressure I thought. Tire pressure should match the weight carried, more weight = more pressure? Thats the idea with those tires, as weight carried increases ... the tire pressure is increased to compensate. The tires have beefy sidewalls to be able to handle that. If you have a "normal" load on the tire and crank it up to max psi that isnt good?