To answer your question why it's making stock torque but not power, peak torque (on a standard k03 car) is at around 2000-2500rpm. However, peak power is around 5500-6000rpm. If it's not making enough torque at 5500-6000rpm, it won't make enough peak power.
So in basic terms, it's coming on boost ok, but then losing boost quickly (this is your boost leak) rather than holding it, as much as a little k03 can, higher up the revs.
This is why peak figures are often misleading, and torque/power graphs tell us the information we really need.
My k03 GTI makes 345lb/ft peak torque at Stage 2. A typical k04 car at Stage 2 makes a similar peak torque figure. But... the k04 car makes about 80bhp more peak power. For the exact reason explained above - it's how long a car can maintain torque as the revs increase that dictates peak power.
A bit like diesels that make 350lb/ft but only 200bhp. The boost is here and gone in a split second, and diesels can't rev high enough to turn big torque into big power.
