Where is the toe and caster with the front in the "up position"? As the front end rises the chassis angle goes level or over center. This will give a greater effective caster angle at speed. If the toe is is correct 2.5 degrees should be plenty. Mine runs 150 straight and true. But you are correct when it gets 10 mph+ head/cross wind it does move around a bit. No toe out at the raised height is key.
Doug