2002 GMC Sierra 1500HD 4WD Trouble

[GMfromAMtoPM]

I’m not the handiest mechanic around so I ask you try your best to simplify your answers. First off, I have the four button 4wd and 4HI, 4WD Auto, and 4LO flash endlessly when I hit them, while 2HI stays solid. 4HI and Auto does nothing, no feeling or sound of engagement or anything, just flashes till I switch it. 4LO flashes but I feel and hear the clunk and it seems to have more torque. Any ideas where to start looking?

[rjgti]

switch or encoder motor