4.11, 4.56, even 3.92 geared rear ends make a difference because they sometimes get the engine running at its "sweet spot" as it cruises along at 70 mph. I have noticed it all my life and have always liked to swap out to lower geared rear diffs to get better performance and often better mileage. Seldom suffered by getting worse mileage. I know it makes no sense but it is true, nonetheless. I think 2009 was the last year to get a 4.8l in a Tahoe and they all had 3.08 gears, I think. I put a set of 4.11s in and the difference was wonderful.
