After modding the phantom, I checked the switches in the Naza software and all is good. But, when I fly it in GPS mode it acts like it has a hiccup on occasion and sometimes starts drifting and not staying locked onto its course. This only happened after the mod. I double checked in the software and when the switch I have set for GPS is up, the software says it is in GPS mode. But it flies erratic and only until I put it in atti does it smooth out. Ideas?