If the truck is off its tires on jack stands and you are in 2wd the front axle will not turn. When the truck is on the ground and you're are driving in 2wd the front axle will turn if you have automatic locking hubs. This is not because the hubs are locked per se, but because the rolling of the wheel is turning the axle shafts freely, this is how you can shift on the fly. With a manual locking hub in free the axle does not spin, you can not shift into 4HI because the rear axle is spinning and the front is not bad things will happen to the t/case. Does that make sense.