Yeah, that's my only gripe with the 6.0, it's a pig! lol!!!
1 MPG difference is hardly a pig.
12mpg city/17mph hwy 6.0l
13mpg city/18mpg hwy 5.3l
5.3l works harder to push the vehicle, hense uses almost as much gas as the 6.0l.
Bottom line is neither one are anything to right home about fuel wise and Yukons and Tahoes were not built for people on fuel budgets.
Owned a Yukon Denali and loved it well I had it, one tip get a good insurance policy with because there are a certain group of people who like them even more...