Seems to be crossed comments between T/O and climb.
On Take Off the the RPM is a function of the CSU
On climb the RPM is a function of the pitch lever.
On take off the prop should not be in fine pitch - it is constant speeding. (Thats how Max RPM is adjusted.)
The original question regarding a low Rpm on take off could be a prop adjustment problem or if the prop is fully fine ( i.e. unable to adjust up) then its most probably and engine power problem