upgrading sway bars should not be necessary. Shocks, sway bar bushings, and end links, and finally springs are what I'd be looking at if you are sure that it is the rear and that you are at stock height.
Sway bar end links and bushings are cheap. I'd recommend MOOG "problem solver" for these items. Generally that line is a solid choice. They can be installed by anyone vaguely comfortable with a wrench.
Rear control arm bushings might be worth a look if those items are in perfect order.
For shocks @ stock height I will recommend bilstein 4600s. They are a few bucks more per shock than all the other junk out there, but I've tried most of the mainstream stuff now and they are definitely the best bang for the buck.
My Denali was scary bad on the highway with blown air ride shocks, and worn out springs, which was the condition when i took ownership
.
I originally installed new gabriel maxcontrol monotubes which helped but those wore out in less than a year. Swapped to 4600s and new springs and its a huge improvement.
I had KYB monomax shocks on a previous truck and gr2's on a car. I have bilstein 5100's on my Jeep. All installed by me. The Bilsteins will be my choice on every vehicle going forward.
