There are many areas to look into.
I would start with checking the collective force with hydraulics in a hangar, with and without the anticipator cable (the one that runs to the FCU) attached. There is a max friction value for this cable in the manual.
On Ariel engines there is also a rather strong spring for the anticipator cable (just behind the aft avionic access door), someone could have installed the wrong spring in the past or at wrong position.
Check the lubrication state (and smooth function) of the "ramp" for the anticipator signal (top of baggage, just ahead of aft avionic access door). Since you say this comes with high CLTV.
Loosing about 10% Tq when turning off the CLTV trim at 120 KTS is about normal (IMHO), check the flight check manual, but having to pull more Tq than wanted to be able to get desired value sounds strange.
The CLTV system with DFCS is weak, this is confirmed by SAC people, and therefore sensitive for problems.
Strange you do not get E37 code on the DFCS in 3 cue, if the system has this much resistance????
CB