If the mechanic knows you are having "low power" complaints, and he sees recent "fault codes" inside the engine's ECM, why isn't he doing something to fix these issues, instead of just uprating to a higher HP?

Are you communicating, to your mechanic about "low power"?  (or are you just telling him, you want to go to higher HP rating, and he doesn't know your true complaint)

When you go back, to mechanic; start with what fault code was recently generated, and see if that ties into a "low power" complaint. (Yes, it may very well be, the Engine's valves and VVAs adjustments and also adjust the Jake brake settings, while inside the valve covers..

It could likely be a Faulty VVA pressure sensor, also, and/or faulty VVA solenoids and/or their connections/connectors, too. {Note: if you or he changes a VVA pressure sensor = they are delicate, and only torque to a light amount of torque = be somewhat gently, with them and don't over torque it.} 


Hopefully, the Fault codes, inside the Engine's ECM memory, will help determine the issue/culprit.