2000 Camaro stumbles when I accelerate

I have a 99 camaro 3.8 my cars problem was that it would surge when I stepped on the gas harder than normal and it did not have power.I got a loaner scanner from autozone and it read that the number 3 cylinder was misfiring, what I did was I changed the number 3 coil and the problem solved. But after that the car didnt seem to have enough power so I checked on the catalic converter and I my self took it off and saw that there was a peace of material that broke off the cat and was stuck on the exit side of the pipe and thats what was my trouble with loss of power. By the way I had to take the car to a mufler shop to reinstall it. Sometimes the fuel pump doesnt work well and it makes the cars run bad. Any way ill tell u this that sometimes 3.8 camaros misfire and the check engine licht will flash then stay on and its normal for these cars to do that sometimes its just a factory mess up in the way they posisioned the spark plugs. Good luck