2006 Freightliner Century struggling sometimes,, then blows out dark smoke

Having some trouble with my truck.... originally all fingers pointed to the turbo charger, however after some tests it shows all is good, fuel injectors also had no issues... i have replaced fuel pump, fuel lines, muffler, cleaned out the tanks to make sure there are no debris. i am out of luck and mechanics go back and forth on what it is... any assistance or experiences appreciated.. .new to trucking so i am lost.

 

Detroit.... yup... another mechanic stated thats what it was. the EGR Valve.... hope that seals the deal on those mechaci issues

 

so that was fixed and issue has gotten a bit better but its not gone... still struggles at times, loses a bit of power and still some black smoke. Would you consider replacing all fuel lines?

 

thanks for the link...i will give a try until i am running. right now we are sitting duck again. its really kicking me on the behind... we have replaced the EGC, Turbo charge, Fuel pump/lines. and we are grounded right now. i have ran out of ideas on how to fix it. the truck continues to stall and black smoke issue is still there. when going up a hill it stalls even more and then blows out the dark smoke, so they recommended the Delta P but that is in real good condition.... any other ideas?

 

that was EGR Valve***

 

60 detroit...