Need Help!!!!Please

I recently moved my 2001 Roush gt from being a garage keep car to it being outside and in the cold. I went to start it up and have never seen a problem like this. The muffler sounds really weird and the idle is funny sounding and it is almost like the horses are gone and I am pushing about 400HP. I drove it and in second gear i could barely get it to 30mph. My first thought was maybe the spark plugs and the ignition is not firing correctly. But it just sounds terrible and I need the car to drive. hopefully it is not something serious.