I have a 1992 GT mustang and it has a slight hesitation when i hit the gas whats the problem?

i know it has a leak in the exhaust pipe. maybe thats the problem? tranny works fine and has no problem when i put it in gear(auto trans by the way) what else should i check to fix this problem. i just want my torque back in my pony. the hesitation is only when i first start out from a stop. if i floor it there is hardly no hesitation.