I don't know what is inside the turret, but I would be checking or replacing the turret encoder, and also checking the condition of any delicate coupling that might exist between the encoder and the turret spindle.
If the turret locks into position with a curvic coupling, of course, the encoder feedback needs to be properly phased in position so that the curvic coupling does not come down on top of itself. It could be that a very delicate adjustment of the encoder coupling is required to improve the turret positioning before clamping.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)