To everyone who doesn't understand why his hubs wouldn't engage, those auto-hubs won't engage after you're already stuck, the wheels need to roll a little as they engage.
Seriously flawed, absolute garbage design.
If you can convert to full manual hubs, not only do you gain the ability to use 2-low, but for the terrible inconvenience of getting out and twisting the lock knobs you WILL have 4WD when you need it. They try to make everything just a dashboard button to sell the things...
This is the only thing I hate about my Cummins/Dodge as compared to my old GMC with manual Warn hubs. It's a very expensive fix on my truck.