I have been trying to decide whether to buy a Yukon XL or a Denali XL. The Denali XL interested me due to more horsepower mostly. However, my father in law, who is a mechanical engineer, told me that the AWD system requires fluid transfers which bleed a lot of power and he thought that the Denali with the 6.0 would be more sluggish than the Yukon XL with the 5.3. That caught my attention because why pay extra for the 6.0 in the Denali if your not getting the extra horsepower of the 6.0 to the tires. It looks like my father in law was right: the 0-60 on the Yukon XL is 8.7 seconds and the Denali XL is 9.2 seconds. This is consistent with my test drive of both vehicles. The YXL had better acceleration than the DXL. I got the Denali XL figures from http://www.caranddriver.com/xp/Caranddriver/previews/2000/November/200011_preview_gmc_yukon.xml
The Yukon XL figures are from the specifications in the Yukon XL 1500 section of Edmunds.com.