4000rpm

hi people recently had a coil pack change, was told that spark plugs needed changing, car was misfiring at 3000rpm, so decided to service the car and change plugs plugs have now been changed but car misfires at 4000rpm now thinking it could be a faulty coil pack? anyone had this...

Can anyone please give me some advise as the Seat garage cant help at all. Ive had my LCR for 2 and a half years and love it bits but have always had a slight problem which occurs every few month for 1 day at a time. If you put your foot flat to the board at low revs it picks up speed perfect...