If everything checks out ok, and the frame is solid, I wouldn't hesitate. That motor is just broken in good. The first thing I'd do to it is a timing belt/water pump job. Get a quality Aisin kit with the pump, belts and pulleys. You don't know if it's ever been done, or if it was done with good parts. The 4.7 engine is an interference engine and if the belt gets too old and fails or the water pump lets go, it will destroy it. These trucks can go for 500 thousand miles or more if taken care of.