My truck, a 2000 7.3L, was not "designed" to run on ULSD. ULSD didn't even exist yet.
ULSD may have less lubrication...and may shorten injector life on older PSD.
It has been said that ULSD + B5 (2stroke), the injectors are more quiet and the trucks run better.
But that doesn't mean ULSD is going to ruin your truck. The new additives in ULSD are supposed to still lubricate....some of us just have some doubts....and some of us have found better lubricates.