Hey, not sure exactly, but try this little test. Drive it around at normal
speed and let things warm up...then do this test.

Exit the roadway and make a tight turn at slow speed
(best described as if you were pulling into a Mickey Dee's drive-thru
sharp turns), this will make your front axles and rear axles turn at
different rates; if it feels like the front is dragging across the pavement
with a binding sensation, then its the VC. The VC splits the power between
the front and rear drivetrains in the TC.

Do a google search on NP249 Viscous Coupler.

This is a known problem with the NP249....there are options as to replace it
(VC) or swap in another model transfer case.

Hope this helps you figure it it out....I just went thru a similar
situation....

T