Do you have any of the maintenance history? It's pretty hard to guess at what it might need without that. You current issues suggest a it might be been subject to a lot of deferred maintenance. The 7.3L is no less reliable than any other motor, when it's maintained properly. Unfortunately, as you've probably already discovered, when things need service, it tends to be much more expensive than a typical car.
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2000 E450 dually V10 wagon
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