I hear so much about how cross overs/CUVs/Unibody SUVs are move fuel efficient then BOF SUVs, however every CUV I have ever compared my 4runner to gets about the same, if not slightly worse then my 4runner. It even gets better FE then some of the more sporty midsize sedans, G35/37 for example.
Really the only thing that CUVs have over BOF SUVs are that they are cheaper to produce, have more interior room, and they have more "Car Like" handling, which personally for me is not a benefit.
Several CUV's get upper 20's highway, some are at 30 mpg...
The issue is getting that mileage and still being a good off road vehicle, I think the Eco Diesel Grand Cherokee will be a good start. The Touareg TDi gets awesome mileage but has no low gearing and has wheels/tires/ground clearance not setup for off road.