1999 Pontiac Grand Am Running Rough

Hi maybe you can help me.I recently have started having issues with my car. It started running rough so I took it in to have it put on the machine to tell me what was wrong and why my service engine light was on, they said it was a miss-fire, and that most likely it is my wires. Since then I have changed my plugs, wires, coil pack. It stopped missing but just Wed. Morning it started missing again.I spoke to another mechanic and he had stated that with the cold weather here in Wisconsin maybe I had a little water in the fuel or something creating a small ice partical causing an injector to clog a little. So I dump some Gas line anti freeze in it and ran it about 30 miles and it is still doing it. Could you possibly tell me what it might be.I have also been told it could be a crank sensor, O2 sensor or maybe even the cat is clogged. It seems that if I do it myself or even take it in I will run into the same thing which is what I have already delbt with and that is replace this and that till I find out what it is. But maybe you have heard of this so I don't have to go this route. Thank You for your time. John