I use the Futaba S-3010 servo in all of my giant scale airplanes. The latest of which is a 43 pound 80cc powered Cessna 206. My only stripped 3010 servo happened when a friend lost his balance and kicked the rudder, never any issues inflight. Did you use the correct servo horns? Trouble shooting a similar problem a you describe on friends new 1/4 Super Cub revealed he had the wrong servo horn on his aileron servos and they were slipping n flight.