I personally like thee max pressure for my 4x4. I'd rather feel a bump than wear out my sidewalls.

 

on my tires the max is 44psi. i had them at 35psi but in a larger truck like mine, i run 40psi. it does tend to get better gas mileage with a stiffer tire. for me i drive on the interstate 80% of the time so i went with 40 and have stayed that way. when i use to work at discount tire we would load all tires at 35psi unless they were a 10ply or higher. car tires we would set at 32psi, even though max was 35psi. anything over a 2500 i would max out. if you go from a P rated to a LT rated i would max out as well. the heavier tire runs better with a stiffer sidewall...either way, check air pressure at LEAST once a month.

also, i bumped my pressure up last week and i went from 14mpg to 14.3mpg..i'm happy with this as long as it isn't going the other way

 

I follow the door placard (35 psi). I bump them up if I'll be on the highway for a long time (38 psi or so).