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Depends on the tire. Check your sidewall for max inflation amounts. If you do all highway, you could knock some pounds out and get a better ride and avoid wearing the center of the tire out.
But some tires perform better at full psi (Goodyear Regattas II) while others do better if you operate them 2-10 lbs under. Check with your tire dealer for the best poundage in your tire for your truck.
Just don't under inflate them and cause the sidewalls to build up excessive heat.