All the other suggestions sound good to me, although...

I found I was having a similar problem my Eagle 2 trainer, the pushrod for the throttle runs inside a nylon guide, from the servo, to the fire wall... When I was throttling up and down I was losing up to 50% of the servo movement in the flexing of the nylon tube and pushrod...

To combat this I actually fibre glassed the nylon guide to the side of the plane, so now it won't move at all, there is no loss of servo movement from play in the pushrod and changes in the throttle settings are instant and smooth as the pushrod can't flex anymore...

Cheers

Matt