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Jack it up and see if you have any side-to-side or top-to-bottom movement in the wheels. If so the outer bearing can be snugged up and sometimes take care of it. More than likely bearings in my opinion.
Are the tops out or in? If they are in with the TTB setup it could be spring sag. If not check the ball joints, too. Jack it up a little and put a pry bar under the tire and move the tire and look for play in the ball joints. There should be none.
Assuming when you say bow out, your tires look like this / \ when looking at the tires from the front of the truck.
Have a front end alignment done. If there is not enough adjustment to cure it, it will require camber bushings. The shop will tell you what degree bushing is required.