hmmmm maybe you could check for different deflections. By that I mean make sure your left elevator isnt throwing more than the right if they are split. If they are not split make sure there is no slop in them from one side to the other. Also look for the same with your alerons. Spacewalkers are low wing planes right? Are you CG ing the plane inverted if not you should be if its a low wing plane. Also is the fuel tank full or empty? That too might make a difference. And lastly what kind of power source is in it? An under powered plane especially one like that, they dont take to slow speeds too well and that will make it respond as you say yours is. What size is the plane, how much does it weigh and whats the engine size you are using?