Diesels putting out black exhaust is usually incompletely burned fuel and one of the causes can be what your product cleaned up. 227,000 is a good start. I don't expect a big expense until the injectors need replacing, hopefully not before 300k.
I sure hope your miles per gallon number are while towing a tall camper. I get ten on average driving 62 mpg, 11 at 55 - 56. 17 empty at 65 mph, but I have a dually with a 4.10. SRWs usually do better.
'11 Eagle 320RLDS '02 Ford F350 DRW 7.3 PSD
"The world will not be destroyed by those who do evil, but by those who watch and do nothing" - Albert Einstein."