front tires are wearing off one inch of tread on inside of tires on 2004 Ford Explorer Sport Trac

had ball joints replaced front wheel hubs replaced and alinement done with brand new tires put on after this was done

If both outer edges of both front tires are worn it would be a sign of excess "toe in" of the wheel alignment. Basically both front tires are going down the road with the front edges looking inward too much. Have a wheel alignment done perhaps the tire shop you have used have not had there equipment calibrated recently. The alignment figures should make it obvious if there is a "toe set" issue, or camber issue.
Thanks for the info but i have had two different shops check the alignment they say it is good they cant explain why the tires are wearing the same on both tires