I'm running WITHOUT rear swaybar (though I do have one on the front) on RAM3500 with flatbed camper (maybe 2,400 lbs of load, including the flatbed??). The truck has custom Alcan leaf pack and 2.5" diameter ADS shocks. I don't notice any unpleasant "lean" while road driving, and I value having the unresricted full flex of the suspension while off-road.
The only time that I notice slight movement is when I am at camp and moving around within the camper shell. If I move forcefully, I sometime notice a slight feeling of "being on a boat" but it's not a big deal. Maybe this would be eliminated with the addition of a rear sway bear, but it's definitely not worth the tradeoff of compromising off-road performance, especially since the on road driving manners are already excellent without.