96 GXE AT Shift Issues

I have searched the archives and found similar problems but nothing that seems to match mine exactly. I think maybe the FSM has too much info but is really handy to have. Anyway, two days ago on the way home from work my Sentra spontaneously decided it doesn't want to shift from 2nd into 3rd. If I rev it high enough it will slip a little and sometimes engage but down shifts very easily. Changed fluid and adjusted on the throttle wire (although the instructions in the FSM were a little hard to follow) to no avail. Does anyone know of a common problem (hopefully a simple fix) that would cause this?

BTW, this forum was invaluable in solving my oil usage problem. The little gasket in the valve cover was the culprit and I can't express my appreciation enough for the helpful advice I found on NissanForums.com.

Thanks for any help,
Charles