David,

There's nothing wrong with your plane. An aircraft is supposed to climb at full throttle, if its been trimmed to fly straight and level at half throttle. The increased airspeed creates increased lift. That energy has to be accounted for by either climbing or, retrimming the surfaces to redirect the energy. The reverse is also true, If you trim the aircraft to fly straight and level at full throttle it will want to dive at anything less than full throttle.

David S