It's recently been serviced with new plugs, leads and fuel filter but.....
Had been running on 90 RON but now on at least 95 RON, 98 when I can get it.
all suggestions welcome...within reason.

cheers
Under load, should have said that to start with, sorry. It's free revving all the way up when not under load, doesn't miss a beat.BrennyV wrote:Could be coil as Matt mentioned also check the plugs are correct for your car (i know it sounds simple)
Also is it braking down under load at that rev range? or all the time?