If it's a remap your after then talk to the man recommended above.
Changing to decat should not loose you power unless something has been done wrong or changed.
An MY97/98 should be fine, although sometimes the decat can cause overboost / boost spikes which the ECU then tries to correct or trigger fuel-cut if the spike is very high.
The MY99/00 is a little more tolerant.
If you just want it to run right then check these hoses havn't been replaced with shiney new silicon, and make sure Hose No.2 still has the brass restrictor in place.
If it does have the restrictor in place are you able to confirm what boost you are seeing ?????
If it's boost spiking then do as I mentioned above. Take the restrictor out and enlarge the hole in it by about 0.1-0.2mm.
YOu can run without the restrictor but you will only hit about 0.5bar (around 7psi) boost.
