These questions about the unreliability of a Ford 6 liter PSD and the expensive 'fixes' to maybe keep it going.... come up with some regularity.
I think I would try to unload it and look at replacing it with a used Duramax or Cummins...or a Ford 6.8 liter V 10....one ton truck.
I believe the OP was retired or close to it. I'm retired and as a result try to keep my costs down and not embark on anything that may have a prior history of expensive fixes or costs.
But that's me. Everyone is different.
BTW....I'm not anti Ford. Have had many thousands of miles driving their commercial trucks (years ago) and have positive memories of their durability.