When I look at the photos I see some things that I know is not good.
1. you are using red Sullivan flex rods and they flex! They are only good for small slow flying 0,8cc-3,5cc powered airplanes.
Instead use either pull-pull, thin steel fishing lines or carbon fiber tubing.
2. You do not have contra nuts on the treads on linkages! This makes more play in the clevis due to play in the treads.
3. A rule of thumb is to always use as short servo arm as possible and as large elevator arm as possible.This is to avoid excessive play in the servo gear.
In your photos I can see that the elevator linkage is mounted way to much out on the servo arm and that the elevator arm is way to short.