did you change the coil packs or just the plugs
have a look on my website
http://www.polarperformance.co.uk/coilpack.html which will show you what a really knackered pack looks like.
any sign of breakdown or hairline cracks under the rubber boot are a good sign they are poor performers.
Although they can still give a weak spark even without cracks due to their age.
approx £200 per set.
Does it drive OK under 3,000rpm with less then 0bar boost i.e when still running vacum rather then boost pressure (assuming you have a boost gauge). If it does and onls mess's above 3,000rpm and when boosting ifnot coilpacks it could be the MAF. The ECU goes from closed loop fuelling using the lambda sensorto open loop fuelling using the MAF at this point.