Hi all,I have a precesion aerobatic mxs that was given to me.The plane has had some repairs to the motor box.when flying at a constant speed I can trim the plane for straight and level flight,however when I increase the speed the plane dives and when slowing it climbs.The cg is per specs.Do I need upthrust or down thrust to correct this? The battery is secured and the servos and linkages are solid.