Check your O2 sensor and make certain that it has not grounded out or the wires came in contact with the exhaust. When was the last time your replaced the sensor?
Disconnect the MAF sensor. If the car runs better, then clean the MAF and try again. If it still runs rough after plugging them MAF back in check this thread and test the MAF http://www.gmforum.com/t279320/
Check for vacuum leaks and repair them. Spray carb cleaner around vacuum lines while the engine is running. If the engine revs higher when you spray in an area, that where you have a a leak.