Rick,
Cal Willis has the best set up i've seen for a Chevy. Also probably the most expensive fix. The secret is that it is a two tier system. Nice stock ride when you have no load and extra muscle when you are loaded for bear and a much reduced sag. Those with Stable Loads on their thick, stiff lower overload springs do get less sag but have to put up with diminished spring travel and a pretty harsh ride. Remember that a pack of thinner leaf springs have a better ride and much improved spring travel compared to a single, thick 'overload' spring, upper or lower. Air bags? I'm not a fan as they have that annoying recoil. But, they are infinitely adjustable; works for many and is a fairly easy add-on. An antidote to air bags would be very stiff shocks like the Rancho 9K's on 9 or KYB's. In my experience, the stock Chevy shocks ARE very stiff and seem to last longer than Dodge or Ford factory shocks.
There are lots of ways to proceed. Take your pick. Emulate folks who have had great success.
regards, as always, jefe