Jumping out of third on a 56 A7SS

[ianselva]

My A7 has started jumping out of third when driving hard. It is OK on the overrun. Before I take the box apart , I'd like to have some idea what to expect . I expect it to be either the selector fork worn or the gear itself.  If it is the gear ,is it possible to grind back the dogs or must I buy a new gear if available ?

Thanks.
Ian

[duTch]

 Mine's sometimes does same if I change up without care, and then load it up a bit, like on uphill.
  Seems it (shift lever) requires to be held in place and with slight throttle manipulation for a slight 'second-movement', if you know what I mean....?
Maybe something to do with those 'extra neutrals'....?
 If I come up with anything else 'll give a holler..
         Cheers