99 Ford F-250/F-350 Super Duty 6 Inch Lift Kit Zone OffroadZone Offroad 1999 2004 Ford Super Duty 4wd 6 Inch Suspension System. The newest offering for the leaf sprung Super Duties is built around massive 9 leaf full height front leaf springs. The leaf springs thin, multi leaf design provides a great ride while maintaining heavy duty nature of the Super Duty. By making the springs out of 9 leafs we are able to keep the spring arch low which improves the ride. In addition, when the springs get loaded down, all