When assembling the tail, i check every piece as i put it on for smoothness. Starting from the tail hub and blade grips, tht they turn freely with no bearing grinding or lateral play. The working from there, the pitch arm, pitch slider, control arm. Then check the pitch slider moves freely on the tail shaft. The control rod and finally the links move freely on the balls. Once you now these are all individually working smoothly, connect up the whole system and move by hand as Tony said. If its all running well, then any binding has to be in the set up either manually in the control rod length or servo arm/ball link. Or in the TX menu travel adjustment.
Good luck