92 cummins stuck between 3rd and 5th help

[jcp dodge]

I have a 1992 dodge 1-ton dually 2wd and the tranny is locked between 3rd and 5th how hard is it to fix any ideas

 

[Stangshcky12]

I'm really not sure just throwing this out their but it may be a problem with the lock out ring for reverse and chances are the trans will need dropped