Re: Problems with new kit...
In order of expense, lowest to highest:
You can get a rear sprocket with more teeth. This will give you more torque, less high end. If you haven't yet added an expansion pipe exhaust, and plan to keep on with this bike for a while, do that. You'll get the more power you're looking for, and probably get more top speed out of it. Lastly, a shift kit to transfer the drive power over to the pedal chain, so that you can take advantage of the multiple pedal speeds.