Towing with a Hyundai Santa Fae

I tow Swift caravan with a Santa Fae fitted with self leveling suspension 2010 plate. I load the caravan so as to have a nose wieght of approx 80-90 kg (max is 100kg)  The problem I am having is that when I am traveling on an uneven road the back of the car seems to jolt quite violently. The car was checked and it was found that the rear shockers were faulty, but this still happens even after they have been replaced.