I doubt your GM OEM 1/2 ton wheels are rated for those higher pressures. Better check before over inflating them.
I would run them at 55-60 psi when towing and 35 psi when not towing with no more axle load than you have..
My 2500 Dodge/Cummins has the same size Michelin LTX AS LT265/70-17 E and is a much heavier truck than your 1500.
This truck front axle weighs 4220-4280 lbs under the Cummins. I found 65 psi works best empty or loaded.
The trucks rear weighs 2860 lbs empty and anywhere from 5200-6000 lbs loaded depending on which trailer I'm using. I found 45 psi when empty and 70 when towing works out best for this combo.
Once you get the tires mounted drop by a set of scales and weigh your trucks front and rear axles separately....then figure how much psi you need in them.
