Chock the wheels, set the parking brake. Unhook your shift linkage at the transmission end.
Try to move the gear selector on the transmission, try to move column shifter next. This should help find your culprit but I'm guessing something in the column isn't happy. Maybe problem with a previous repair in the column.
I can't think of any vehicle that's designed to not go INTO park or neutral, under any conditions. All the usual interlocks prevent going OUT of P/N.