ORIGINAL: EXT2Rob
Jeez......you've replaced everything, but the problem still exists. The only other thing you haven't replaced is the servo.
Maybe something is going on with the servo, and it's drawing too much power and ''browning-out'' the BEC. I had a servo do this to me once. Got a spare servo sitting around?
+1 this
might not be anything wrong with the servo might be one of those pulls insane current ones like the savox that could cause the browning out.