2002 SVT Ford Focus Issue

I recently had an "accident" on a freeway. As I was attempting to go around someone, I accidentally downshifted into a TOO LOW of a gear and sent my RPM's off the scale. The car over revved, and shut it self off (white smoke was seen comming out of the back of the car as well). I pulled over and did a quick general inspection and noticed my CAT glowing bright red. The car still runs but I have the following OBDII codes: P0141 and P1131. The gas mileage has gone down considerably, horsepower and torque is now suspect and when the engine is cold, it hesitates and misfires. After it warms up a bit, it drives fine. What gives? Could the O2 sensors be causing this problem or is this privvy to something more serious (bent valve). HELP!