It’s a 2nd gen, it’s also 91 octane, thanksIf its 3rd gen 2015-2018, its 91 octane, here is a link that will tell you octane for all gens of 6.0
What Kind of Gas Does a GMC Sierra Take? (All Generations Explained) | DrivingYard
GMC Sierra can use 87 or higher octane-rated gasoline but if the GMC Sierra is the type that comes with a 6.2 Liter engine, then, 93 octanedrivingyard.com