I have a 2007 Mustang GT, cool intake, long tube headers, straight pipe exhaust and just the other day I put a tune on it. When I picked the car up from the shop the engine and everything seemed to be running a lot better. The dyno test showed that it was pushing 280 at the wheels. Today when I was coming home from work the engine seemed to run like it had resistance. It really felt like that the engine wasn't getting all it's power at all. RPM seemed to be higher than normal and not matching up with the speeds. I know it's not my clutch, because when I go through all the gears in low speeds it seems to be grabbing all gears. I have noticed that there is a lot of road vibration lately that haven't been there until I replaced my tie-rod ends. Could my input bearing going into the differential cause resistance when speeding up? I just need ideas on what could cause this intermittent issue. I'm almost thinking it could be an injector going out in it, but then again I think if it was an injector running weak, it would have shown up on the dyno.