Does anyone know what causes the brakes to grab while towing? I am trying to figure out if it's the travel trailer or the truck. When I come up to a traffic light after braking I let off the brake and when I apply the brake pedal again I get a jerking motion. I have had this happen in stop and go traffic too. Could it be the ABS braking system on the truck? I have had the brakes checked on the trailer. The brake controller is set on 3. It does not happen all the time.