the OEM rear shocks really do take a beating off road, and they lose their strength fairly quickly....your shocks might not be blown, but they might be severely worn, causing the extra body roll...so, they might be absorbing enough to not be riding a roller coaster down the road, but can still give out on sharper turns, etc., producing the body roll
when i removed the front shocks on my '00 at around 45K to put my ranchos on, i was able to press them in with 2 fingers, yet i didnt have any extreme body roll, even with the swaybar off