I was reading on edmunds, and supposedly when they did the "full test" on the gt500, they could only make a 13.4 pass and a trap speed of 108. They contacted ford who told them that approximately 3,500 gt500's possibly have defects. they blame it on a delaminating air filter. ford later gave the exact gt500 back to edmunds with a proper filter and it made a pass of 12.82 at 113 mph. also with the proper filter it gained 16rwhp. so if ya have one... check it out. it could be a defect. dyno it.
"There is no replacement, for cubic displacement"