Driveshaft is starting to slip hence the burning sound - with your miles I'm 99% sure that is the issue, especially since you said it was becoming hard to move and hearing crunching.

Park the X and get under and drop the shaft, I guarantee the splines are super worn. If you don't strip it out all the way you can get away with just an extended shaft, if it strips out completely, you'll need to rebuild the Tcase with a new output shaft as well

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards