As a former owner of a Ford 6.0L I would bet it was a combination of the inductive heat strategy programming in the FICM and the failure of the FICM that ruined your injectors. The 6.0L had a serious cold start and rough running problem and Ford "solved" the problem by reflashing the FICM to heat the injector coils so that they would function better and the truck would run smoother when cold. The injectors were never designed to do this and it leads to early failure of them. I had at least 3 injectors going bad when I ultimately traded my 6.0L because I didn't want to spend the huge $ on that repair and an increasingly bad bedplate leak.
As others have suggested the biggest issue with your truck with B20 is rubber fuel components.
