vacuum leak or fuel system?Long

[richie]

I didn't change everthing at once,but over the course of many months.I always think my stang is running good then all of the sudden the car will run a lot stronger for a very short amount of time.A example is yesterday on the freeway at 70 I barely touched the gas and the car accelerated up to 80 plus two to three times as fast as usual.Then I slowed back down to 70 and got on the gas and there wasn't nearly as much power this time.My car jerks sometimes slightly when accelerating.