My truck did the EXACT same thing a few months back. It didnt have but about 75K on it either. I had everything checked out that was possible, but in the end, had the head gaskets replaced and found a really small, almost undetectable crack on one of them. Ever since I had them replaced, it has been fine. I will say one thing though, be sure the mechanic re-adjusts the valves once everything is installed. Mine didn't get adjusted and they rattle like hell.