Good choice going with a 2.4 system. Is that an Airboss ESC or Flightboss? Never had issues with Airbosses before. Try a 12 x 6 prop. Have you checked amp draw on 12 x 8? Might be overamping ESC. Can't remember what mine was pulling ampwise but it's worth a check just to make sure. As I recall 3s=13 x 6.5 or 14 x 7, 4s=12 x 6 on the Torque setup you have. Is it surging all thru flight or at the end of the pack? Might be LVC set on soft cutoff telling you it's time for the hanger if it's towards end of pack.