When I picked up our Armada, the dealer I got it from specifically told us to use 87 octane. I found this weird for such a powerful engine. Since the truck came with a full tank, it gave me a few hours, LOL, to check the manual before we needed to fill up again. Sure enough, the manual says 87. So, that is what it gets. I tried 93 and found that the gas mileage decreased. With 87, I consistently get 12-13mpg city. With the 93, it went to 10! I drove normally during the period as the truck was new. Now with 2000 miles on it, we are still using 87 and mileage is bearable for a truck of its size and power. All and all, I love this truck!