Originally Posted by BBoxster

It was a private road not the highway!! I said it happens in every gear not just 5th.

To confirm:-

In every gear the acceleration dies off at around 4500rpm. There are no strange noises or anything else untoward that happens just the fact the car will not pull past those revs. If I change to the next gear the car accelerates well again until it hits that same 4500rpm.

Thats it I`ve described it as best as I can.