My 2009 2.5 litre turbodiesel pathfinder has recently started surging when I am going up hills... Initially it started happening randomly only around the 2500 rpm range however it seems to do it now when the engine is warm and between 2000 and 2500 rpm. I noticed today when I was going up a hill and it was doing this that it was also blowing a lot of black smoke... it only does it under load and any other time drives fine...