loss of power and heavy black smoke

I suspect you have significant coking in your EGR system and Turbocharger. This is not uncommon for this vehicle, as unburnt Diesel coats the components. There is a baffle kit that can be installed to reduce the amount of coking that builds up. And, it is advisable to add cetane boost to your fuel regularly to help burn the fuel more completely. However, in this case, the damage is probably arleady done. The EGR system needs cleaned. The Turbo will likely need disassembled and cleaned, and the CHRA (central housing rotating assembly) must be checked to see if it can be salvaged. The unison ring in the Turbo may be stuck too. If the turbo cannot be cleaned, it will need replaced. This is an educated guess about your concern. Clearly, you could have other issues, such as injector issues and the like. A good diagnosis from a 6.0L specialist is vital going forward to give you the best possible resources to maintain and repair this otherwise strong engine. Good luck!

INGECTOR PUMP.