There are several possible causes, here's one to check easily:

With the engine not running (hold car in place with foot brake) move the shift lever slowly, with the catch button held down, from park to #1 and back.

You are checking for a feeling of a "double click" as the gear indicator moves from one gear to the next.

There are two places where the "click" is created: One in the shift lever mechanism and one inside the transmission. The two are normally in synch and seem as one. If the transmission moves a bit there can be two clicks.

If you get two clicks on any gear, next thing to check is the motor mounts and the tranny mount. Check also the connections on both ends of the rod connecting the shift lever to the tranny shift lever. You may be losing a grommet on one end thereof.

Do those checks, post back with results.

Good Luck,

Bob

:>)