Lack of power at 3000rpm

I have a 2007 Freelander 2 diesel. It pulls well normally, excellent mpg, no smokey exhaust and I'm generally very happy. However, I've noticed that if I'm in 4th and the revs creep up to just under 3000 I lose all further power no matter how far down I press the accelerator pedal. It doesn't slow down just no further power. It doesn't do it in third. Not tried it yet in 5th and 6th.

Possibly a turbo hose, but somebody will be along soon to give better advice.

first things first , air filter blocked ? fuel filter choked ? injectors mucky ?