You could always try the torsion bars and leaf springs from the Suburban 3500.Well actually it's roll stiffness that keeps the truck controllable. And you can do roll stiffness other ways as well. I used to do a bunch of autocross when I was younger and there's always a debate in suspension tuning about whether you go with sway bars - or with increased spring stiffness. Each has their own drawbacks and advantages. After driving the truck this way - and I have driven it on the highway - and it seems fine .. I wonder if it might be better to maybe add some more roll stiffness into it with stiffer torsion bars and maybe the addition of some of those Timken load things. (forget what they're called). For the time being it's an interesting experiment.
One truism I’ve found over the years is that manufacturers are never going to waste money on parts that an engineer could reasonably argue they don’t need. If GM could’ve achieved the ride and handling goals they were targeting with simply stiffening the springs, they would have. My bet is that they know something about the handling of these in certain circumstances, that we don’t, that caused them to spend the additional money to add the sway bar.