My 21 Denali with 22" wheels is getting 24.8 for my best 31 miles averaging 72 mph using cruise. I've put about 1,000 on the truck since getting it 3 weeks ago (few 200 mile trips lately). My normal commute it 9 miles one way, 36 a day with lunch I had been seeing 16.5 on those trips. Overall I'm showing 18.5 a cross my 1000 miles. I'm expecting that to settle in around 17 with my "normal" driving. I'm really surprised at how well this truck does on fuel economy. I normally run 88 octane (seems to be an MN thing).