It's difficult to suggest any solution for this without knowing which
engine is in veh.Most common being the 5.0 or 5.7litre, I'll give it a
shot based on those two. They were known to have upper and lower
intake gasket leaks.The bulletin read that gaskets were inferior and
would degrade around 60k miles.I would suggest checking your engine
oil and see if it has a foam consistency and check the level of your
coolant.They may point to head gasket or intake gasket leaks. If oil is
foamy, head gasket.If coolant is low, oil good , intake gaskets.Also,
are the spark plugs foweling out ?Is it difficult to start ? It wouldn't hurt
to check those intake gaskets for leaks.