Yup. Viscous coupling in the t-case is locking up. Mine does it too, as do almost all of them.
My fix... Run without the front shaft, reinstall it if you know you'll need 4wd, like if there is snow coming, or a field party that night.
I gained 4 mpg, and it drives and tows better 2wd.
Only 1 issue, the creep. It will creep forward an inch or two after you put it in park. Also sometimes there will be a jerk when stopping or taking off. Both due to the front output of the t-case loading and unloading, no big deal really.
....Then to fix it right there is the manual shift part-time t-case swap, it uses the Borg Warner 4406 from an F150, and Expedition driveshafts.
...btw good luck finding a good Awd case, or the coupling. The couplings can be bought, but are $600+, + the seals and rebuild.