increase payload capacity 2004 Suburban 1/2 ton

Air Bags on the rear axle and high quality tires are about all you can do for changes. I would suggest you have the suspension aligned and have them check to make sure the front suspension and brakes are in 100% condition.

I would suggest you add a B&M or TruCool auxiliary transmission cooler--best $150 insurance you can get. And add a new set of very heavy duty shock absorbers.

That's about all you can do to improve your vehicle.