The waviness can be many things. Something as simple as the boost not holding steady be it the wastegate or boost controller settings (gain, limiter, auto learn logic, etc...) Knock as well. A good way to find out if its knock or engine noise is to log the ignition timing albeit it with Cipher or the dyno equipment if possible. The timing will always start to drop off at the top you just want to make sure it does it according to the IGN maps. Cam timing also plays a good amount (overlap, etc) so VVEL could be it. Although some forced induction VQ37s look smooth as a baby's butt. A good test for knock if logging is not possible is to throw in some 100 octane and see if it smooths out. Logging fuel pressure would also be handy if a pump is having trouble keeping up and also calculating injector duty cycle. AFR would be a good indicator of this.
Also like Phimosis mentioned the way the car is strapped down and the ability for the clutch to hold the power can have an effect. Typically when a clutch slips the graph will look much different.
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