How big is your Gw2.dat? That sounds a lot like the symptoms I had when my Gw2.dat had gotten huge and fragmented. Deleting it and letting it rebuild cured the issue for me. Note that when you delete it you’ll lose the email and password from the launcher, so make sure you know what they are before you delete Gw2.dat.
Right click the Guild Wars 2 application and select “Show Package Contents”.
Navigate to: Contents > Resources > transgaming > c_drive > GW2 and then delete Gw2.dat.