My vehicle is actually a Navara. Excessive black smoke on acceleration

What is your question?

When I accelerate the power lags and then picks up with plumes of black smoke coming out of the exhaust. I have had the EGR replaced by a diesel specialist but this has failed to sort it, cost £700.00 The vehicle is only 2010 and has 35k on the clock so it should be fine, I am getting really frustrated with it know as no one seems to know what to do.