94 mazda protege dx 1.8l sohc power loss
 

One day I was driving out of town and my car started surging like it was out of gas, but my charge light kept flashing. So I thought it was the alternator, bought a new one and it did the same thing. Bought a new battery, same thing. I traced all of my wires and found no problems. It will stay running great until the battery runs out then it will only idle. I'm at a loss. What could be causing this?