Broken 4wd!!!

[Armadillo6.0]

I have a lifted 2006 f350 diesel cc sb and I put a 6 in lift this summer along w 20 in wheels and 35 in tires. I didn't have a problem with the 4wd till this winter when I was using it more n more. It would make a humming sound and vibrate the whole front end. I took it to my local dealer and had them replace the u joint for the 4wd almost 2 months ago and I have rarely used it since then. On my way to work last night during a winter storm I heard a loud clunk and got out it was broken....I feel that this is because of the angle it is at because of the lift kit or what. Any advice film other lifted truck guys would be awesome

[Armadillo6.0]

How do I fix this so I dont break it again?