2009 freightliner cascadia nightmare

My husband purchased a 2009 freightliner cascadia and it has been a nightmare ever since
he was able to work for 2 days when it stared loosing power to the point to almost shut off
we took it to the shop and they replaced the reman ITV and the MCM on it and he was able to work
for three weeks then the truck stared losing power again and blowing black smoke, we have taken
the truck to a couple of repair shops and they have already replaced the fuel pressure regulator, the doser block
the snober fitting at the doser block, both fuel shut off valves, a doser injector, the fuel water separator, the fuel filter,
the ATD sensor harnes, the DOC inlet temp sensor, the DPF mount gasket and clamp, all 6 injectors and they cleaned the
DPF filter, the truck is working better but it is still blowing black smoke (mostly when heavy loaded) any ideas???
The mechanic told us the DPF separated and moved but he sent it for cleaning and was able to save it, how can we tell if the DPF is working properly.
Thank you.

 

The first 5 times we took it to Freightliner repair shop but every time it took them about a week and a half for even minor repairs and they did not fix the problems (besides they were charging an arm and a leg) now we are taking it to a small repair shop.