Probably an issue with the way the car was strapped down and may have moved some causing the strange graph. Watching the videos every car moves. They did a crappy job strapping the cars down which accounts for the discrepancies.
Properly strapped down car on a dyno looks like:
BTW - the numbers posted are STD which will always read higher than SAE. I would say you are around ~368WHP/TQ with SAE readings which is in-line with what I put down in my 2010 SS.
I laid down 430WHP/377WTQ SAE in my 2011 GT Friday before last.
