Having problem with front diff. 4x4 working. 4- low dose not engage and know 4- high dose not want to stay engage and cluncks

What is your question?

what might be my problem with my 4x4 front diff. 4- low you can hear the solenoid engage but just a whirling noise. And know 4- high dose not stay in all the time. This a 2005 GMC sierra 4x4 2500 HD auto trans