5th gear unseen obstruction.

OhioYJ

As mentioned, there is absolutely an adjustment procedure in the FSM, it's much wordy than it needs to be. If you look in this picture below you can see the plate that needs adjusted:



There is a pin on the shifter that touches that silver plate:



If you get the plate too far over it will not be able to go into 5th or 6th. If you leave the plate too far over the other way you'll be searching for 5th and 6th. You want the pin to just barely touch the plate essentially. There is a section in the manual on this.