doeman, I had a simmilar prob when my b400 was new. After 2 mins on a new pack the esc would go into voltage cut off and reduce power. If I landed and let the esc reset it would be ok for a little while then repeat. I loosened my belt and ran some more packs and it fixed itself. E flight suspected a bad esc and sent me one but it hasnt done it again???? Double check your belt tension. How old are your batteries??