Steve, I'm very sorry to hear about the situation. I've been through a similar Scenario more than one time so I understand your frustration. I was stranded in Miami once for 6 hours on a Sunday... My car had been disassembled more than once and I always noted grounds and things. I have lots of documentary pictures. There are actually 2 grounds up front one on each side. There's also 1 on the rear transmission and some other ones located throughout the engine bay.
After many hours of testing my tech found some issues in a wiring harness in the center console. after it was replaced in never happened again.
One of the unfortunate issues with the new GT is the complexity of the communication network and the number of modules. If you recall Ford boasted the GT runs more lines of code than a F-22 which sounds good but if you have one issues where a module losses communication with another there is a domino affect that can spread to other modules that can make it really difficult to track down these problems.
Good luck my friend..