I see you are a rookie and this might be considered necroposting. FYI for the future. Ford Mustang Forum - Announcements in Forum : 2011 - 2014 Mustang GT Tech
Make sure that the install did not include 02 sensor wiring extensions. That is a big no no.
Also check for bananas in the tail pipes.
X- pipe 2" from collectors? Ratchet straps to remedy sounds awful. So evidently the JBA with the X-pipes were 2" shorter than stock headers and H-pipe and you would have had a 2" gap at the over axle pipes. I don't see how the heck you could get everything to fit with being 2" off. Something does not sound right. Maybe you were exaggerating a little or they sent you the wrong X-Pipe or headers or both?
2013 GT, Track Pack
, Recaros, Kooks Axlebacks, Airaid CAI, BMR Rear Adj. LCAs, BMR Relocation Brackets
, JLT Oil Separator(s), Barton 2 Post Shifter Bracket
, Steeda Motor Mounts
, Barton Shifter
, JHR Clutch line, BMR adj. UCA and Mount, Kooks 1 3/4 headers/catted H, DSS Al Shaft
, BMR Loop
, Vogtland Sport Springs front/BMR rear, Strange Adj. Struts/Shocks, Extended ball joints, Steeda Bumpsteer Kit, Whiteline Tranny Mount Bushing, Borla Overaxles, BMR Watts, Vorshlag 3" Ducts