Intermittent jerky towing of 5th wheel

Ah! The Gooseneck adapter to tow a 5th wheel with a gooseneck ball. Yes there should be chains then. Also, check all around the 5th wheel pin box where it attaches to the overhang of the 5th wheel for stress cracks. The adapter puts extra leverage on the pin box and can lead to failure of the 5th wheel chassis structure around the pin box. Hopefully this isn't the case. If the area is all enclosed and hard to see the chassis, a pull test while watching the pin box might show any movement. Any movement would be abnormal. Many if not most 5th wheel manufacturers don't approve of gooseneck adapters.