[TheMattPraha]

Bought a GT 2004 diesel 1.9, what revs should i be changing gears at for this engine?

 

[rgwm]

Depends how you want to drive- they are pretty torquey low down, and although you can rev them round to 4500 or more, there isn't a lot of point - you'll go quicker using the torque.

In my 147 1.9 JTDm I tend when accelerating briskly to change up about 3500, and rarely end up using 4th or 5th gear - just slot straight from 3rd to 6th.....

When travelling around town it'll pull in any gear from 1000 rpm or so, although 1500 is probably better

 

[dgmayhead]

Drive it like a taxi and never go more than 1500rpm. However, don't rely too much on the torque to pull you around if you're in a hurry as it'll mince your clutch.
Agree the sweet spot is between 2000 and 4000rpm. It actually sounds alright as well when not at tickover.