What does this mean?
Determine if the arm is actually loose on the shaft, AND FIX THAT
Or does the arm and shaft turn together but rather there is play somewhere as inside the trans.
There are cases where the internal "comb" has come loose from the shaft. That may be your trouble.
With the link disconnected, you should be able to "snap" the thing from gear to gear, and there should be "very little" play in each detent.
Various destructions for adjusting linkage is in the service manuals, which you can download FREE at MyMopar. Some of those came from the guys here at FABO
http://www.mymopar.com/index.php?pid=31