The 7.3 Powerstroke engine will probably go down in history as the best diesel engine ever used in a pickup truck of any brand. They are very troublefree and can easily last 500,000 miles
I have owned 14 of them, all purchased with over 225,000 miles on them, and used them daily with no problems.
Many of them I later sold to friends. They all are still going strong, and most have well over 300,000 miles on them. In fact, recently I bought one of them back again. It is now my daily driver, and has 331,000 miles on it. Still runs great and has lots of power.
You can not go wrong with a 7.3 Powerstroke that has been serviced regularly.