I am guessing this is without the engine running?

I had an issue with an elevator, when flying the tail would jump around when in straight level flight.
So I tried to get the surfaces to wiggle on the ground and figured out with full throttle the elevator would flutter.
It turned out to be prop wash flexing the surface and not the servo issue. The servo wouldn't move at all.
I havent fixed it yet but at least it isn't a servo issue.

I guess in a way I am asking have you checked everything? Including swapping the servo to see if it was the servo?

Good Luck with your trouble shooting