teh triangle stock you are seeing is a tailbrace. it simply strenghtens the tail section and is not of use for smaller planes. i would agreee that your control rod is either flexing, or your servos is getting overloaded. to increase the torque, try going to a 6 volt pack. if not, get a higher torque servo, the plane in question i assume is an aerobatic plane. try doing the same thing at 3/4 throtle and tell me what happens