P4Pro gimbal tilt/pitch droops

I have calibrated the gimbal a couple of times. After using the C1 button and returning the gimbal to the horizontal position the gimbal slowly tilts slightly downward (maybe 5 degrees) and then comes to rest. The tilt indicator on the controller screen remains at the “straight ahead” mark even after the gimbal has come to rest. Any suggestions for a fix appreciated. Controller issue or motor fatigue? Something else? Thanks!