What causes the outside shift rod (one closest to leg) or linkage to stay stuck inside of shifter box and not allowing me to shift from forward to reverse, until I take a screwdriver and manually push it back?

 

try adjusting the linkage, put machine in nuetral, remove the nuts that connect the rods at both ends, adjust rods so that the ends line up perfectly with the holes at all 4 places, that should help, also there is supposed to be oil in the shifter. it may be dry or could have gotten water in it causing it to rust inside, it comes apart, if you have a service manual it explains it.