I was having a similar problem with my st-1, All I did was replace the steering servo with a higher torque model and it corrected the issue. I realize that might not be your problem, but if it were me thats where i would start. Check the saver aswell, if you havent made a parts order yet i would get one of those. Sometimes they will cause these issues. If I think of anything else Ill stop by and share it with you.