Question: using your hand are you able to shift the trans into park by pushing on the linkage at the trans? If so then it is the cable. It is out of adjustment because it has probably broken. This is a PITA to fix as the new cable runs under the carpet and through a grommet in the floor. Actually takes about two hours to replace...but what a PITA to do.
What happens is the clip that holds the adjustment is in a plastic body. The plastic body has broken so the entire cable moves instead of pushing or pulling the shift linkage.
Did I mention that this is a PITA to replace....
Mine broke one night for the wife...and after two weeks of putting trans in neutral, setting parking brake, crawling under to push linkeage into park...I had enough and replaced the cable.
Got mine from Rock Auto.
Good luck and oh....have fun.
2002 4dr 4wd S10 Blazer