Began having the following problem with my P2V, 3 axis Zenmuse gimbal, GoPro3: After flying just fine for 2-3 minutes, the Phantom begins to lose height, eventually hitting the ground. During this unexplained descent, I still have full control of yaw, pitch, and roll; just won't hold height or ascend even with left stick full up. The blades are still spinning, it's just as if the Phantom doesn't have enough "oomph" to stay up. It does not appear to be trying to return to its RTH point, just comes straight down. The batteries are at least 75% full. Happened with several DJI batteries. I can start it up again, and it will ascend correctly, and then after a couple of minutes the same thing happens. I thought my batteries all had a little swelling, so I pitched them. Got three new batteries: Limefuel, Ofeely, and no-name - all brand new, no swelling. Same thing happens with all three of these. Tried switching to new 9443 props - no change, still falls after a few minutes. Any thoughts?