Here's the 2010 Mercedes Benz GL350 BlueTEC. BlueTEC means it's a diesel. It gets roughly the same fuel economy as a Chevy Tahoe Hybrid. The complexity of a hybrid isn't needed. The VW Jetta Sportwagen TDI is another great example - 42 mpg highway, again nearly as good as a hybrid like the Honda Insight. Why get a hybrid, diesel is better.
Diesels make sense in fire engines and Ford F-450s but a luxury SUV? Yep, 400 lb-ft of torque means the GL350 BlueTEC is not slow and at the same time the V6 is smooth and only a little noisy. Benz's gas engines are quieter but with 23 mpg on the highway you'll hardly have room for complaint. The interior is exactly what you'd expect from a Benz - lots of leather and plenty of gadgets. Too expensive, right? Maybe but the base price of a diesel powered GL350 is about $59,900 - add some features and the price can hit $70,000 or roughly $5k cheaper than a Toyota Land Cruiser. I'll take the diesel Benz.