I would not think that the servo's are your problem. You say it needs retrimming all the time. Is that for turn or climb. I would as suggested check the ailerons. I would also make sure that the push rods are secure for the elevator and rudder. As for the 3003 servos they are famous for some slop on the top end. The 3004 are are the same as the 3003 with the exception of ball bearings. I would check the servo's under a load and make sure the gears are good. Good Luck, Dave