Check your pitman arm! (The arm that goes from the steering box to the center link.)
I've broken 2 of them to date, and when they break, you loose all steering!! Which is something you very much want to avoid.
Also, if it is wearing out, DON'T GET THE CHEAP ONE from O'Reilly Auto Parts... The factory one made it 250k, the O'Reilly one made it 27k of the same style driving... So I'd recommend shelling out for a name brand at least, if not the OEM part.
If it ISN'T your pitman arm, and you have a friend you can bug for 10 minutes, there is an an easy way to find out what it is. Simply crawl under the front of your truck, and have the friend rock the steering wheel back and forth within the slop. You can usually feel where the slop ends, or have them watch the front tire while doing it and turn just enough it doesn't move. Then you can easily see where the motion stops in the steering system, and that's your bad part!