Missfire???

[pevil]

Rover 75 1.8i....I normally drive quiet sedately, the car lends itself to this kind of driving as we all know, however yesterday I had reason to boot it a little, accelerating quiet hard in second, reached just over 5000rpm and car started to stutter badly, tacho dropped to 4000rpm, car came back to life and tacho was heading towards the red, changed to third and took her past 5000rpm no problem, thinking it may be a one off I tried again, second gear stumbled at 5000rpm, third gear again no problem and that's the bit I can't understand, surely if it was a coil pack or spark plug it would do it in any gear under load/high revs :shrug:
Any of the knowledgeable experts on here have any idea?
By the way there was no engine check light.

Thanks in advance.