I have a 2013 351DS and found the white knuckle driving very troubling. After having a full alignment (the rear axle was not squared and the front end was way out of Ford spec) the drive improved significantly. However, I was still concerned with the excessive sway and lack of control in high winds and passing trucks. After researching a variety of options, including steer safe products, alternate shocks, etc. I found the Ford Cheap Handling Fix
on irv2.com and thought it worth a try. I had my local Bridgeway dealer make the adjustment and have driven approx 1000 miles since. The improvement was significant and I can now drive with one hand in a moderate cross wind and while passing a truck.
FYI: I also had all the wheels balanced after the alignment while the local truck tire dealer replaced all the valve stems with custom stems (No extensions for me and all easily accessible for checking). Although the balance did not improve the ride as much as the alignment and sway bar change, I believe it does contribute to the exceptional ride.
The alignment cost me $630. Squaring the rear axle was expensive and I had them fix the offset steering wheel (15 degrees). 6 hours of work . I submitted it to FR and did not get a reimbursement. The sway bar change was $200. Tires balanced and new valve stems $340