I swapted a 04 cobra motor in to my 02 gt ran great for 8mthns now I have lost power and when I punch it the car will spit and sputer then take off replaced fpdm,frps, maf, checked my elec connections. It seems to get worse then longer I drive it 20-30 miles or so. No engine light took it to a shop they don't know

 

Its either a problem with your intake, or fuel system... Could be your tune. THe shop you took it to, I hope it was a Mustang guy, and not like goodyear, or Ford directly...

 

I took it to Mustang Muscle in STL When he put it on the dyno it was running very lean 15 all the way across on fuel ratio he added 30% more fuel which took care of fuel problem from 2500-5000 then runs lean I'm running dual focus pumps.