I would be leaning towards t-case since all shafts rotate regardless of t-case setting. How does the fluid look in the t-case? How many miles? How often have the fluids been changed in the t-case and front differential?
2005 SE Off Road: JBA LT Silver ceramic coated headers, Cajun B-Pipes with Heavy Metal Cats, Borla Dual SS Cat Back, Uprev Tuned, K&N Air Charger, CSF 3328 Aluminum Radiator, Grille Craft Upper and Lower Grill, Burtman Rear Air Reflector, Manik SS Nerf Bars, Nissan Tow Mirrors, Bilstein HD's, Moog 81085 Rear Coils, AirLift 1000 Rear Springs.