You've gotten a lot of advice, let us know what you've tried and whether any of these things made a difference. I don't know yet if we can rule out AFM problems or plugged exhaust, or what you've found in your hunt for vacuum leaks. Also, test your O2 sensor, if it's giving a faulty reading it'll screw up your fuel mix as soon as the engine reaches operating temp. For test procedures, check out
Oxygen Sensor Information