1999 Chevy Cavalier Starts fine, then really rough idle, an

I will start the car and everything seems fine. I drive down the road for a block and something happens, like a small hiccup and then no matter how much gas I give it, it has no power or rev up. If I back off the gas and then lightly press I get power back. At idle the car is super rough like a dropped cylinder but when I disconnect the electrical connector from the alternater it smooths right out. So I drove it with this connector disconnected and I never lost power. The alternater was tested good, so what is downstream that could be fouling this up? I just replaced the fuel pump, fuel regulator, and filter, and map sensor. Help please!!