This video may help you understand where the TRS is located and how to tackle the replacement if necessary.
I agree that it seems like a cable / mechanical disconnect at this time though. There shouldn't be easy free play in moving the gear selector lever. The sliding of the shift lever should transfer this movement through a cable to the TRS switch which electrically changes the internal switch arrangement within the device to tell the PCM and transmission what to do.
http://www.youtube.com/watch?v=3inAO9gORh0