The most important thing to note, is that you cannot use any Latitude and Longitude, the coordinates must be those of an existing node of the AFCAD. So, the result might not be what you expected, because if you insert Lat/Lon freely, GSX will find the closest node and use that one.
Also, setting a node, doesn't necessarily mean GSX will push all the way to it. The node should be though just as an "attractor", but the Pushback will stop as soon the airplane is reasonably straight.
I'm not sure what you mean with "just want turn 45 degrees", the program will try to FIT a curve, with an end point to an end node, it will never move straight, otherwise it would be mathematically impossible to solve the geometry between the front gear, the towbar and the vehicle, which includes the vehicle wheels too.
Maybe, if you could give me an example on what you are trying to achieve, I might be able to help.