Sorry that I haven't reply in so long, but I finally have gotten the problem fixed. I talked to a mechanic (30+ years experience), who suggested flushing the fuel injection system, since I had replaced just about everything and he had seen similar problems with these engines. After flushing the system, the car still ran about the same. I took the car back to the mechanic and after checking various things and scratching his head for almost two hours, he pulled the spark plugs and found that one had a hairline crack in the ceramic. He replaced the plugs and the car now runs like new. Keep in mind that the plugs had been recently replaced with ACDelco parts from Autozone. My mechanic told me that the plugs had probably been dropped or otherwise mishandled at the store before I bought them, he has seen this before. So, I probably replaced alot of parts that were still OK, but like I said the car runs great now. Thanks to everyone.