I completely agree, I've yet to find shop I trust, especially dealers. I will keep looking to see if I can find a reputable shop around me. I see you have two 2014 GTs in the family. You've never experienced anything like this with either of them?
See if you can find a local (reputable) performance shop that specializes in Mustangs. If they don't do those types of repairs (many don't), they usually know the best places to get the repairs done.
Don't just call them. Go there and talk Mustangs with the gear heads. They'll likely point you in the right direction.