I would imagine that a good service department relationship often is the make or break deal. First of all, I'd find a dealer that was already "performance-oriented", ask about their own performance parts (if any) and their installation of it. You're giving them business there and I'd find it unlikely that they'd bite the hand that fed them. If you found a Ford service center that was also a FRPP, you might could get a FR500 cat back and a B&M Ripper shifter which is sold out of the catalog. If they install it, my guess is that they are less likely to say that their installation or the parts they sell damaged your car. You may pay more for the parts and installation, but I'd bet that its the most likely way to keep your warranty intact.