Did you try it with the front sway bar alone? That would be next. I suspect the front is a 2-3 times stiffer than the rear and responsible for most of the sway in bumps but it might be reasonable with it connected. Is your truck a diesel? Maybe there's a softer sway bar from the lighter gas version?
Slightly stiffer front springs without a sway bar may work to limit a bit of body roll but it would be pretty much proportional to how much worse the sway in bumps gets. If you have the gas version, maybe try the diesel front springs alone.
A real junkyard hack maybe to cut a slot length wise done the middle of the stock sway bar, between the bushings on the chassis, allowing it to twist more? Probably it will just crack at the end of the slot...