Where are you, Richard? It sounds to me like it could do with the attention of someone who really knows how to set up a banjo, like Dave Stacey in Letchworth, Andy Perkins in Kent, or Helmut Rheingans in Eyam, Derbyshire or a few others. Music shops don't usually have the faintest idea about banjos, even if they stock them, and can do a lot of damage by thinking they do know.
Cheers
Ray