20psi boost is that to high?

[Rumcajs]

Injector trim codes are stamped on the housing/body of the injector and the codes are entered as parameters in the ECU for each and must be correct for every cylinder. So either take it to Bosch fuel injection service joint and ask them if they're able to confirm the settings for each injector or take it to those idiots from Nissan to do this simple check and insist they do it in front of you.
I'm afraid the changes your tuner had done will now make it much harder to track down the real cause of what seems like over fueling.
Remember upping the boost and airflow values causes more fuel to be injected so if fuel metering is incorrect/suspect for example (let say that injector/s are leaking/ trim codes are incorrect) black smoke is evident.
Cheers

Edit: I was thinking about this a bit more I'm wondering what is the rest of the exhaust like if the exhaust manifold is warping from the heat. I'd be checking if the cat is also not partially blocked from all that exhaust soot. Also Nissan had some issues with some CrD model had no trim codes entered in the engine ECU.