Lack of power off load

Hi there I am experiencing lack of power from my 300tdi, I have got snap acceleration, a little whiffy smoke but no slow acceleration it just gutless then Rickover goes lumpy but picks up, snap acceleration then tries to die, I have replaced cyl head, injectorrs are refurbished ones, new lift pump, new fuel filter, looked at boost pin checked metering pin ( was a little sticky), somebody else has messed about with FIP setup but not the timing side of it though, I'm stuck as to why she's so gutless. Any clues please as to what path to take