The TSB that's listed above may not be the particular fix for your car, but the symptoms you've described are exactly what I experienced. The fix was applied to my car and voila ... right as rain.
The issue for mine ended up being a steering rack that had been over torqued in the factory. Once the car was warmed up and at highway speeds, the "stiction" problem would rear its ugly head. At speed, the amount of electric assist drops off (as it should for better steering feel). It's when that assist drops off that there is not enough umph to overcome the slightly too tight situation in the rack.
It may take Ford a little while to own up, but they will. Just be patient and take your new gem into the dealer.
Here's another thread ... 2012 Ford Focus Steering Problem
Oh, and ...
Gold Nugget: '12, 400A, Wintr Pckg, Yellow Blaze HB
Mods: Llumar Tint:35 / 20; K&N fltr + Snrkl Del.; Splashgrds; Grill Pinstripes
Hatch Nation #174