Missfire

Hi All
5 years with my SC now and still love it, but she has developed a hick up (misfire) at 60/70 on motorway if I apply throttle slowly it starts missing it is so predictable ,put throttle to the floor and we get kickdown and loads of power so its not fuel starvation or air leaks injectors have only done 120.000 pump has been tested ECU has new capacitors ,turbo pressure sensor cleaned and filter changed ,turbo pressure checked and correct. It starts first time idles perfect when up to temp and runs perfect in every other way , any suggestions please.

I know you said it isn't, but are you quite sure it isn't a small air / vacuum leak somewhere? One which won't have time to respond to a sudden acceleration but will gradually upset the AFR with slow application? Could be a dried out hose that's beginning to crack.