[shorod]

I'm not sure which engine your Sunfire has and if it has a timing belt or not. If it does, you should consider replacing the timing belt, the belt tensioner, water pump, and have the head planed while it's off the car. Rather than power wash the head you could ask the machine shop to run it through the parts washer while they are planing it. When you took the head off were you able to see evidence that the head gasket was the culprit of the overheating and power loss?

-Rod