My experiences with the magnums (I've owned a few) has not been that experience. As you know, 5.2/5.9 share the same heads. Heads are known to crack, but usually not in a place where it hurts the running. But that doesn't mean yours didn't. If I remember correctly, you replaced the intake plenum gasket ????? ?? Your confident it was white smoke and not blue ? I agree, early indication seems like a head gasket. Do you have dual exhaust? If so, coming from one pipe or both?? Spark plugs will tell a story.
