I also have an 86 K3500, I've posted photos blue upper, white lower. And yeah with about eight bales, or a yard of gravel it's rides better. But since I rarely get more than half it's capacity I run to less with no problems.
On the flip side, if I'm pulling a two horse with a dressing room storage lounge area. Or car trailer on the hunt for grown up toys, everything gets pre trip service.
Seems like hassle but I've posted before about my uncle driving the Suburban with 55 psi in the tires, the headache and loose fillings, we threatened to walk home if didn't let some air out.