I am a newbie to this site. I was plowing about 15 inches of snow this past storm in the Northeast. After the 28th hour of running the the truck pretty hard the 4x4 on occasion will disengage. I don't know the truck isn't in 4x4 until the truck kicks sideways while pushing snow. I can tell only the back tires are spinning so I let off the gas and it slams back into 4x4. I frequently checked my hubs for being hot while plowing and didn't find this to be the case. The 4x4 light stays on, I have electronic shift on the fly with auto-locking hubs. I talked to one guy who has a F-250 and said he had the same problem. He took his truck into Ford and they couldn't find anything wrong with it. As a result he made the diagnosis that his Hubs may have been frozen. I'm not sure if I buy this. I have read that it could be the transfer case, or vacuum seal which I'm not real familiar with. All suggestions would be greatly appreciated. This is a procedure that I am hoping to tackle myself. It would save me some time if in your post you would share with me how difficult fixing this problem is. Thank you in advance for all suggestions. We are expecting another storm here so I may be forced to take the truck in for service.