I notice that you extended the wing tips down and clipped the ailerons at the wing tip. I've heard some where that it helps with aileron flutter? I know my Sweet Stik would flutter when the .46AX was on full throttle, and you gave it a sec to get up to speed. (Probably what ultimately caused its demise.)

However, my 4*60 has ailerons out to the edge, and I don't seem to have any trouble with it. (.75AX in there)

My thought was the bellcrank system just had too much slop in it? Did you fly yours with the kit supplied bellcranks?