Good chance that plastic gearing in the mirror is broken. The plastic gears get brittle and effectively disintegrate with time.
The mirrors can be rebuilt more cost effectively than replacing with new if you’re willing to spend your time tackling the repair.
Check out gruvenparts.com. They sell mirror replacement parts (brass gears, motors, etc) for the GM family of SUVs and provide detailed instructions and assistance for rebuilding the mirrors.
It’s not too difficult to do the repair, but does take time, a little experience and a few tools. The most difficult part is reassembling the mechanism that allows mirror rotation in and out because there is a heavy spring that needs to be compressed and then held with a retainer ring. Be sure to wear good eye protection when working that part of the repair.
Take some photos as you disassemble for reference when reassembling.
I have successfully rebuilt both mirrors on my 2007 Tahoe LTZ.
Good luck.