no power below 2000rpm

hi, i have a 2002 a4 tdi 130 and below 2000rpm there is no power, above 2000rpm the turbo pulls very well in 1st 2nd and 3rd but not so well in 4th and 5th !
ive had many many diesel cars including a 90bhp focus and even the focus had more power below 2000rpm.
i have changed the maf but didnt help, the car has been mapped to 170bhp but it is not the map that is the cause because it was like this before the map ,after the map it just has more power above 2000rpm.
no fault codes have appeared on my £25 ebay scanner.
i have to drive over 2000rpm or the engine labours, any ideas anyone ?
im thinking maybe a faulty egr or knackered/sooted turbo but the turbo seems to work fine in 1st 2nd and 3rd above 2000rpm.
there doesnt seem to be much torque as the car needs to be revved like a petrol to accelerate.