The biggest problem with the tail is the spring effect caused by the tail pitch slider. weaker servos struggle to centre against the torque of the spring.
Second biggest is the tail rod guide, which will not line up smoothly if you use a ball link on the servo.
Disconnect the servo and move the control rod by hand slowly. you will feel if there is a spring effect.
This means that the little screws are too tight. BUT if you loosen them, SLOP will develop.
I took a dremmel and made the holes oval (lengthwise). Then I tightened the screws to remove slop and checked that there is no spring.
There after clip the rod into the tail rod guide. Leave it loose at the servo side line it up and you can see how much it will bend to meet the ball link. if it is alot, then you will have to make up a tail rod guide or put on the z-bend.
hope this helps.
I see plank flyers!!!