On Ford Chassis:
Check for steering looseness, check for proper weight, check for proper tire air pressure, check all sway bar bushings and if it has an extra hole to rear of the vertical link move the links to the rear hole, check for track bar on front axle the tag axle will act as a track stabilizer on the rear, check for bad shocks and check for correct ride height.
Sway is mainly controlled by the sway bar system so that is of main concern...moving the vertical links to the rear holes will add to the sway control...be sure all bushings are in good condition and if not replace them.