With 340 lb*ft of torque, I don't really see having only four gears as a huge issue. Seems like a reasonable way to save a few bucks on the base models, IMO. Besides, aren't the Denalis and Escalades coming with six-speed boxes?
Overall, the new design looks great. I drive a previous-generation Denali & Yukon XL quite a bit, and while they're nice vehicles, I'm not crazy about the dated interior design, leather that looks, feels and smells just like vinyl, and the unacceptable amount of squeaks and rattles for vehicles with less than 100,000 kms on the clock.
Sounds like GM has a winner with the new one. While I won't be in the market to purchase one, I'm definitely hoping that the boss picks up a couple of used 2007 Denalis when they start to come in off-lease in a couple of years.
