Why don't you just post the code?
Or are they just telling you this and you are repeating it back to us?
Misfire code should be a P030x series number...
The last digit is the cyclinder that it is misfiring on.
The exhaust manifold is your stock headers.. If they weren't removed when you put your test pipes on then you shouldn't have a leak there.
Here is an example of using the Internet if you have the code number
OBD-II Trouble Code: P0300 Random/Multiple Cylinder Misfire Detected
No need to post with exclamation marks as if you were yelling when people are trying to really help you.
If you are that inept about mechanics, take it in to a reputable local shop.