I totally rear right over the engine overheating when I read it originally. I would definitely lean towards a bad water pump, is they are most definitely a wear item on those diesel. Head gasket would be very unlikely on a 7.3L unless you REALLY overheated it and kept pushing on. But that would be a consequence, not a root cause.
That said.... Has your engine been receiving periodic "SCA" (Supplemental Coolant additive)? These are extra nitrates which prevent cavitation. Some 7.3L's have had holes worn through in under 200k miles because SCA was not used.
