That is a nice setup
Well, tail issues can be simple, or they can be involved.
Anytime I have a tail issue of any kind I first check the mechanical setup. Make sure the tail pitch slider is moving effortlessly. Check for binding in the grips. One place i have seen issues a lot lately is in the Teflon shrink on the tail control rod. If it isn't completely shrunk onto the rod, or has air bubbles this can cause binding.
Take the control rod off the servo ball. how freely does the control rod and tail slider move? You should be able to hold the heli vertical and the weight of the control rod be enough to move the slider. I am ok if it takes a slight shake to break friction, but it shouldn't be tough.
I am also curious what your Parameters menu D is at. The default should be Red or medium. Might try bumping that up one and trying gain adjustments again.
Vibrations are another possible factor. The BeastX likes to be mounted hard, i have seen guys actually use a zip tie to hold them down, just put fuel tubing over the zip tie so you don't damage the case.
Hope this helps.
