How do you eek out nearly 30mpg and a 600 mile driving range from a big, rugged honest-to-goodness SUV? You give it a Diesel engine. And that's exactly what Range Rover is now offering shoppers of their most lavish vehicle. As the Land Rover lineup continues to expand, it’s still the Range Rover model that resides at the top of the luxury SUV mountain. The $85,000 entry price says it …