Problems in transmitter, transmitter is slow in a closed loop what could be the reason

If transmitter show slow response while a closed loop and when we put the controller on manual the problem is rectified, so we can say the problem is in?

a) valve

b) positioner

c) transmitter

d) A/M Station

A/M station (In case of failure of A/M station, controller continuous to work in auto mode but A/M station will receive input from DCS (4-20ma) but not able to provide o/p in auto mode but we can change o/p with its front panel. A/M station provides the rate of change in o/p better in Auto mode than in manual mode so after its failure it works in manual mode.

Isolate the Tx drive a signal to the DCS with your test equipment if the DCS performs well Check the Tx parameters some already referred damping. simulating the sensor offline If that passes Check the final element ( positioner) maybe calibration maybe not. stroke it and check the travel and tuning with transducer if that passes Check the logic program whatever software they have for that system