Go to the link provided above, you will find many posts regarding this. One of the important things to know is that Ford now approves of the modification.
When I did mine, the improvement was dramatic. Went from two hands on the wheel all the time, to be able to easily keep it on the track with one hand. I know, you should keep both hands on the wheel (I am a former law enforcement driving instructor), but tell me who doesn't occasionally use one hand.
I had mine done when I got my front end aligned, and it cost me $40.00.
Happy Trails, Forrest