Tread wear to the outside of the tire center is usually caused by excessive positive camber (top of the tire tipped outward). That can be caused by worn king pins and/or king pin bushings. Stand back from the front of the vehicle a few feet and eyeball the tires. If my guess is correct, you should be able to see a slight tipping of the tire out at the top. Jack up one side of the front at a time, grab the tire top and bottom, and try to rock it back and forth. If it moves, check the wheel bearings and the king pins and bushings for looseness. Changing camber involves bending the axle, so be sure all the possible loose spots are covered before looking for someone to do that. A few heavy duty truck alignment shops still bend axles, but some of them won't work on small trucks.
Jerry
