I hear and feel a thunk when I hit the gas hard. Someone told me it was a bad motor mount what do you guys think. If it is a bad motor mount how much will it cost me to get it fixed and do think its affecting my performance at all.
It is most likely a bad motor mount. It shouldn't cost too much to have replaced. I have never done it on the Mustang but on other cars it was somewhere near $200 or so installed. Get it replaced soon if it is the motor mount. Too much rocking in the engine bay can wreck other stuff like your tranny.