It will most likely be your toe adjustment. It appears to be too much negative toe. Toe has the greatest impact on tire wear. Especially since they are wearing the same. I doubt your ball joints are worn out that much, the same, on both sides. In order for your camber to do that, it would have to be way way off. These trucks are rarely that far out. A "good" alighnment shop would be able to tell you for sure. Most tire shops don't do camber adjustments, due to the work involved.