When trying to select a portion of audio, it either selects all or the selection jumps around.

I just loaded up my old version of CS6 and audio selection works as normal--I click and hold on a spot, drag and release.

Perhaps you could give us some details of whether you're in Waveform or Multitrack view and what steps you're using to select part of a clip.

Depending on how much you mean when you say jumps around, if it's only a little bit you might want to look at the Edit/Snapping menu and either turn it off or choose a selection that suits you better.  However, snapping only accounts for small jumps so I only mention this as a first thought until we hear what you're doing.