Malcolm I flew at a contest last week and I noticed several of the planes dancing around in the wind also. Luckily my Nuance felt locked in and extremely stable. I want to just throw a few ideas out there. Is it possible it could be your transmitter elevator pot or a bad servo? When I set up my Nuance I followed BJ Parks setup recommendations to a T. I love the feel of the plane in the air unlike any other I've ever flown. Maybe look up his setup recommendations and compare them to yours.
Evan