Pickuptrucks.com has much more information about the suspension on the Sierra All Terrain: Longer double wishbone front suspension, 11+ inches of suspension travel, special Fox shocks, jounce shocks in place of bump stops, electric swaybar disconnects.
http://news.pickuptrucks.com/2010/12/first-look-gmc-sierra-all-terrain-hd-concept.html
http://news.pickuptrucks.com/2010/12/first-look-gmc-sierra-all-terrain-hd-concept.html