2002 Chevy suburban transfer case issues
 

My 2002 Chevy suburban feels like constantly in four-wheel-drive with slow shifting and loadbearing feel. Four-wheel-drive tree reads 2 high, but at approximately 40 mph there's a grind and sluggish feel. Would really like some help to narrow down what the possible issue is. Please and thank you.

Additionally, transfer case was replaced at approx. 250,000 miles. Currently has 313,500 miles on vehicle. Engine still runs like a dream, but this mysterious tc issue is different than last time it went out. Regardless, still fairly certain it is the tc or related.