I am looking at buying a 2004 Escalade AWD ESV with the 6.0L. Does anyone know if it requires 91 octane fuel or is it just recommended?

i have an 07 with the 6.2 in it i run 89 in it with no problems at all. you should run the tank almost empty then get like a half tank of regular and see how it goes if it dont run right fill the other half up with super