Hey welcome to FTE! First off, when you get a chance and or extra income, ditch that K&N filter- they are too open an element for turbo diesel use. There are tons of other intake filters and systems available that won't destroy your turbo.

If your fuel pressure is good, and you have no leaks on the intake side, have you checked for leaks on the up-pipes yet? A leak there can casue loss of power. And like the others said, if you can find a way to check your ICP or pressure the HPOP is putting out, that may help some. Please gives us any more info you can, and stay tuned to FTE and enjoy all the savings from learning here on FTE!!