Thanks All for the replies, much appreciated. I did drive the car for about 2 hours after I picked it up from the dealer - mostly highway. It runs and sounds fine.
Yep the Genesis dealer is totally incompetent. The root cause was a bad junction block that is easily accessible from the trunk. They replaced two wiring harnesses and a fuse box, and some other stuff that I can't remember. Finally, they took a systematic approach and determined that the junction block was getting 12v in, but only 2v out. Unbelievable. I don't know anything about electronics, but it seems pretty dumb that they didn't attempt to trace the problem logically. Love the car, hate the service.