It could very well be a failing bearing. A good way to get an indication of the transmission's health is to do the following:
Fluid change, examine fluid for paste/shavings, examine magnetic drain plug for bits of ferrous metal (if you have one)
Remove the (usually) green cover on the end of the trans where the T/O bearing and finger are and inspect for any kind of paste. If bearings are failing this seems to be where the remnants collect. Keep in mind that you'll need to replace this cover as it is usually destroyed when removed.
Hope this helps. Good luck.