Did the misfire start after you changed the spark plugs, or was it doing that before you had the plugs changed?
In case the Techron doesn't help, here's a company I have heard good things about when it comes to fuel injector cleaning:
http://www.witchhunter.com/
I might take the extra step in swapping the injectors between cylinders to see if the high rpm misfire follows the injector, but that might be more than you want to tackle.
I can't really think of what else it can be, unless its an issue with the vario-cam system turning off at the higher rpm point, which I believe is right around that rpm point. I think you would need someone more knowledgeable about the nuances of the electronics system to chime in.
BC.