Hi Scotty I have a 2011 f 350 6.7 power stroke with 120400 miles on it.  The four wheel drive will not engage from the inside of the truck. I just recently had the vacuum lines replaced along with the front locking hubs and had the four wheel drive module replaced inside the transfer case. I think that’s where it is. When I have the hubs in auto the four wheel drive will not engage. It sounds like they want to but I just hear a humming noise. When I lock the hubs in lock then turn it to four wheel inside the truck the four wheel drive will engage but I still hear the humming noise. I have no clue what else it could be. I was hoping you had an idea of what you think it could be.