Take it to a performance workshop with a dyno and get them to check the Air fuel ratio as you do the dyno run, they can also check for detonation. That will give you a complete picture of what is wrong.
Plus you get to find out what power your mods make. -post here with results!

You want flat spots, I've got flat spots!!



Looks to be a problem with teh BBM switching over from short to long runners.

(ignore the peak power, that needs looking at too!)