99 tahoe help plz
 

I have a 99 tahoe and I recently had 4x4 issues where it would not lock in 4hi or 4lo the front tires lock in but tcase doesn't so I tried awd option works and works almost flawlessly I replaced tcase guessing it was faulty same issues gonna loose my mind how can awd option work but not 4hi or lo the case itself in 4lo changes gear ratio you hear and can feel it but will not operate front shaft HELP PLZ

Nevermind I traded it in for a dodge