We had the head gasket replaced, ran fine for a month, now the antifreeze is pumping out of the reservoir when I'm driving. Doesn't happen at idle or when the engine is reved in park, only when your driving. I ran the overflow tube into a container while I was driving, it pumps out about a gallon in 10-15 minutes of driving. I think the head gasket is blown again the pressure from the pistons is forcing the antifreeze out the reservoir?