Lil Buck. Have you put a body lift on this at any time? If so, like previously mentioned it is common for the tunnel floor to not allow the shifter to move far enough. Usually this is a high range 4wd issue but we don't know if you venture off road...
Try all the detent fixes described first, then you need to go internal. Shift forks sometimes wear a lot not allowing complete engagement of the gears (since the shifter won't move the gear far enough). Also, extreme thrust washer wear will keep full gear engagement from happening.
Hope the adj detent from Jon at JBCustom Fab fixes it or stacking a few small washers as spacers to increase the spring pressure is a simple fix for you.
Good luck