By Brandy McDonnellThree-time Grammy Award winners Pentatonix, including former University of Oklahoma student Kirstin Maldonado, appeared today on “Good Morning America,” where they delivered a stellar live performance of their a cappella cover of the Charlie Puth hit “Attention.”“Attention” is the opening track of the multiplatinum-selling vocal group’s latest album, “PTX Presents: Top Pop, Vol.Read more on NewsOK.com