4 low won’t engage because the gear indicator won’t show it’s in neutral

Scan it for trouble codes. Sounds like an electronic issue of some sort. Expect a faulty sensor or weak electrical or ground connections somewhere in the system.

Hello your nautral safety swicth needs to be celebrated .put key turn to on but dont turn on engine.place it on nautral ! If you can get a friend to sit in truck while you go under the driver's door and face nautral swicth .disconnect shft rod .look at swicth you have a nut on left and one on right side loosing them both just a bit more the right side. Then make sure truck emg- break are on and blocks truck may move be careful! Using your right hand push right side up or down after you tell your friend to turn engine on make sure his foot on breaks aswell when truck turn on with key on nautral turn of engine put not to move shift.loosing rod put dont move position. Lock nuts then fasten rod your done