violent bucking on 2002 Saturn L200

when the car reachs 30-50 mph it violently bucks....really hard it shakes the passengers. what is causing this?

Asked by for the 2002 Saturn L200
Could be quite a few things, but I would start by thinking of a torque converter shudder - (automatic transmission, yes?), since you have a speed sensitive concern. Have a qualified technician road test with you to provide an opinion of direction.