The pitch case (68211) will usually be too tight on the main rotor shaft (68203). This will cause drag on the motor. To fix this, put a 3mm drill bit into Dremel, then put the pitch case onto the drill bit, then run the Dremel at low speed for about five minutes. Hold the pitch case very gently to prevent it from spinning around. After this, lubricate the inside of the pitch case with some graphite to further reduce friction.
The M2x6 screw which holds in the pitch bellcranks (68212) will usually rub against the flybar control levers (68209). To fix this problem, put the M2x6 screws into a drill and hold the head of the screw against a metal file to shave down the screw head. This will prevent the screw head from rubbing against the flybar control lever.
Some CP upgrade kits include an older style flybar (68208) which is not very good. The older style flybar is completely smooth and does not have the grooves stamped into the flybar to prevent the control arms (68209) and flybar paddle (67371) from slipping. If you have one of these flybars, you should replace it, because it will be almost impossible to prevent the control arms from slipping on the older flybar even if you roughen the flybar.
The Piccolo CP/Pro head has some cyclic interaction. For example, when you apply forward cyclic, it tends to go forward and left, and back tends to go back and right. Therefore, you will need to use aileron/elevator and elevator/aileron mixing to compensate for this problem.