Okay there are many things it can be like OFK said. I'll tell you how to diagnose and figure out what the problem could be.
First start by jacking the front of the truck up on the driver side.
Now that you have the tires off the the ground, grab one of the tires at 12 and 6, and see if you rock the tire back and forth. If the tire moves and feel like it's rather loose when you do that, then you probably have a bad ball joint.
Now grab the tire and 3 and 9, and repeat the process trying to rock the tire. If the tire moves a lot in that direction, then you probably have a bad tire rod end.
Another thing to do is crack the tires all the way to one side, and visually inspect all the bushings on the A arm. If you see any metal on metal contact then you need to replace that bushing.
The odds are that it's either the ball joint, or tie rod end causing the issue. There is a chance that it's your steering rack and pinion, but it's probably something simpler than that.
Once you get the vehicle you can more easily diagnose the problem buy pulling off the tire and yanking out the tie rod end and seeing how loose it is...and can look at hte ball joint more closely.
Hope this helped!