Do you have the Bell-Hiller head? I have discovered it is possible to snap the drive links on with the mixer levers flipped upside down and it will almost look right but it will behave sort of as you are describing.
Also see if your pitch curve is symmetrical. That is, in idle-up you should have -12 at low collective, zero at center stick, and +12 at high collective. Then when you go to normal mode it should be slightly negative at low stick and up to full +12 at high stick. (If you are using the stock transmitter.)
And for sure check the bearings as bzinfinity says, and the shaft endplay (should be zero).

And if you are using EFLite wooden "symmetrical" blades look carefully at the airfoil. I have had two sets that I swear were flatties mounted upside-down, they weren't even remotely symmetrical. Of course this will make the power seem different from neg to pos pitch.

(sorry, now I see you are using the CF blades, good for you, they are more accurate)