I would be very upset at this point, but if they can actually get the car right, and not take any further delays, I would allow them to fix it without too much complaining, and take my future business to another dealer even if it were 40+ minutes away. In my opinion, it sounds as though the people working on your car are incompetent and most likely have not worked on another 5.8L Shelby motor. That aside, it still sounds like they do sloppy work, and have some of the worst customer service I've ever heard about.
Regardless, when everything comes together, I'm willing to bet you will enjoy your car again, but I would keep on these people at least once a day asking for updates on the car. Make it clear to them the price tag, the amount time they've had it, and the poor workmanship you've witnessed ( with the coolant leak, and misdiagnosing the problem twice now ), and demand attention to the car. I haven't read through all of this, but have you spoken to the GM or owner of the dealer?
Regardless, when everything comes together, I'm willing to bet you will enjoy your car again, but I would keep on these people at least once a day asking for updates on the car. Make it clear to them the price tag, the amount time they've had it, and the poor workmanship you've witnessed ( with the coolant leak, and misdiagnosing the problem twice now ), and demand attention to the car. I haven't read through all of this, but have you spoken to the GM or owner of the dealer?