Gimbal works fine until Pitch is panned up or down...

Hi guys, I have setup the gimbal using K. Garrison's GUI settings and have run into a problem. The issue occurs whenever I try to pan the pitch either up or down the motor jerks back & forth. This stops when I center the pitch from the taranis as seen in the following videos:

http://m.youtube.com/watch?v=hi5Ku6FYILk

http://m.youtube.com/watch?v=kcuagIFRvw4

The videos show the issue occuring on the camera and the other on the gui. How can I eradicate this issue? Please help...

I have connected the fc pitch & roll to the naza m v2 & F2 ports and rx pitch & roll to the frsky x8r channel 5 (X1) and channel 8. The Naza is on an S-bus configuration. I have S1 & S2 swtches allocated on my taranis to control ch5 & ch8.