Hi guys, new to the site. I had the same problem. It felt like a dead spot in the steering. Do you notice your brake pedal locking up as well at the same time. The power steering (ATF) fluid became contaminated somehow. It has something to do with the hydroboost system.
Reviving this old thread, as my 08 F350 4x4 has the same problem. Tires pull the wheel back and forth in the middle of long turns at highway speeds, both left and right. New tires did not fix the issue and it does it whether braking or not. Truck has 168,000 miles and I'm sure front suspension/steering components are worn, but steering seems tight otherwise. Wondering if anyone has a specific fix for this issue.