We have worked on tons of them in my shop, 2 are in here right now for head gaskets and cracked heads. I don't stock much for new parts here except oil, oil filters and 4.7 head gaskets and timing chain sets. The symptoms are exactly what you describe and typically begin after overheating because of a faulty water pump or radiator. The 4.7 can not stand to be overheated at all, pretty much instant failure of a head gasket when the gauge goes over 1/2 way and 3/4 pretty much means cracked heads.