drevil nailed it. You didn't triangulate your links. Your upper links should meet at the center of the gearbox. This will keep the axles centered instead swaying from side to side like yours are doing now. There's several mounts you can buy to do this or you can devise your own. Here's a few:
http://rc4wd.com/shop/product_info.p...oducts_id=1039
http://rc4wd.com/shop/product_info.p...roducts_id=915
http://rc4wd.com/shop/product_info.p...roducts_id=792