Truck switched to 4 low on its own.

OP:
Take it to a different dealer for a second opinion if he or you are uncomfortable with the first dealers opinion

 

easy, client systems...

the guys are just having fun since it's a preposterous question. if it actually locked into 4L while going down the highway, stuff would be broken. a more likely scenario is that if it's an off road, someone bumped the rear locker button and panicked when the lights came on the dash. that would not hurt anything since it didnt attempt to lock up. people have enough of a hard time actually trying to get it into 4L and locked when at a standstill and reading the instructions. it will not even go into 4L when flipping the dial over from 2H while at a stop. it requires certain steps to make it happen.