[Shotimes] AXOD, code 647

[van Oss]

AXOD with 75K miles, tranny flushed about a month ago.  After flush, car 
felt very smooth.  I'm getting code 647:  "Transmission problem -- unable to 
obtain correct gear ratio for third gear."  Fluid is good for level, color, 
and smell.

My wife reports a clunk/thud when she shifts from Park into Reverse or 
Drive.  Started about 10 days ago.

Any ideas or shall we go straight to rebuild?  Anything I can check or test?

VO