R' David Cohen: <<I think RYBS said "Shir haMaalos: miMaamakim" during 10 Yemei Teshuva, but said it before Yishtabach, as part of pesukei deZimra. (We did this in my high school.)>> I think Ner Israel (Baltimore) says it immediately after "Avinu Malkenu" because of hefsek concerns. Michael Hamm