Years ago I used a Hellwig rear bar on a 1994 C2500LD and it seemed to help out a lot. This was the lowered black extended cab shortbed you've probably seen in other posts. It was dropped, front suspension fully rebuilt with poly bushings, then I added the rear bar. All that combined with the low profile tires, the truck handled a whole lot better than you should be able to expect a truck to handle.
What I liked about the Hellwig kit for that application is that it was strictly bolt-on, and they included two sets of end links for stock vs. lowered trucks.
A previous GMT400 I'd done the AddCo bar and it required drilling 4 holes in the frame for the bar bushing brackets, and the end links were sized for stock height so if you were lowered, they sat at a bad angle until you replace the bolts with appropriate lengths and cut the sleeves down.
Richard