7.3 is definately a proven motor. My work has 3 6.0's. Can't tell you the years off hand but can say have had nothing but problems with them since day one. Turbo's, head bolts, head gaskets, egr's, and even trans problems on one of them. I drove one of them when they first got it (just to see how it compaired to my 6.5 chevy_ which by diesel standards isn't much of a diesel) and I was not impressed at all. I myself would look another direction (brand) or try and find a 7.3 with lower miles. My dad has a dodge (04) and I would have to say that is a pretty impressive truck. Well for a dodge anyways.....If you are looking at one and thinking "man this thing is alot cheaper then anyother diesel I am looking at" there is a reason for that.
When I bought my 6.5 I knew it wasn't the biggest, or best diesel out there. But for what I paid for it and a little upgrades (about $2500) I have a truck that will run both mileage and towing with my dad's 04 all day long. And about $15 grand less into it.....