You have the stopper tight on the servo horn? Some might gasp but I always leave mine just a touch loose so that the stopper can turn in the hole on the servo arm. This keeps it from bending the servo arm when you give it full throw. I do put a dab of thread lock on the nut holding the stopper on the arm to keep it from backing off.
Is your elevator horn in a stright line with with ur servo arm? Cause depending on how you mounted it to the elevator horn the shortness of the push rod and being on a angle at full servo throw will cause that. If thats the case youll see a twist in your servo horn to