Intermittent loss of power above 5k RPM

[quantumsheep]

At the ripe old age of 33 I recently bought my very first car - a lovely 2000 Porsche Boxster 2.7. The car is in excellent condition and seems to have been cared for by it's previous owner (only 1 owner car!), however I'm having a strange issue.

The car runs brilliantly for the most part, idles well and if you drive like a granny (which the previous owner was) you'd never notice anything was wrong. However, sometimes, if you go above 5k rpm the car loses significant amounts of power and struggles to gain any more revs. There's no CEL, either.

The strangest thing is that this issue only seems to occur every now and then, not every time I drive the car.

What would be the first things to check? Any help would be greatly appreciated.