onthefly

This is the scenario. I've got the Funtana, and just put in the Saito 100 after having an OS 120. With both engines there is glitching or chatter in the tail mounted servos when at or above 1/2 throttle. Doesn't happen in ailerons or throttle. I've gone through the plane with great detail to make sure there were no metal to metal contacts. I've got the Futaba 8UAF and the rec is a futaba fm rec'vr. Tail servos are S132H ( not looking right now). I even replaced the tx and rx with JR PCM century 7... same thing happens. I've bypassed the switch, checked connections. Do longer leads have inherent problems? I had the Sig Extra 300 with even longer leads to tail mounted servos with no problems. I remounted my Dad's sopwith pup with servos in the tail with no problem. Am I missing something? Can an older servo cause this? I don't really want to put in larger, slower servos...
Ideas?

Thanks