Only one transmission guy seems pretty common in my neck of the woods; however, I'm unsure what classifies a dealership as large. I also feel like a dealership knowing you're tuned, opens the opportunity for a dealership to push for a payday. Once they have that knowledge, you better hope they're ethical, because it would be easy to tie all kinds of diagnosis to the tune. Also, once you make the claim and Ford denies it, you're left with no leg to stand on. You can't go to another one and shop around. If you find a good one that will work with you, first thing is be honest with them, and then ONLY give them your business and none of the others. Hopefully capitalism will eventually prevail. Best of luck with your situation. Remember, built Ford tough.