A6 diesel auto estate...lack of power
 

I have an A6 2.5 diesel auto estate..02 reg...he has no power when pulling through gears or pulling away at a roundabout..i have to nearly get to 2000 revs, just to pull off...been on scanner,box ok,no probs with air mass sensor,egr valve etc..showing no faults at all....doesnt leave black smoke whilst driving or when youput your foot down...Has an members any ideas??..will appreciate any info and thank you for your time in advance..Carrno.....