So far about the only advantage a fullsixe hybrid SUV has over a normal gas SUV is increased city mpg. If you look at the specs for the hybrid Chevy Tahoe and compare them to the gas Tahoe the hybrid is heavier but it gets something like 21mpg in the city as opposed to the gas only which gets 15mpg, and they both get the same mpg on the highway.
What it comes down to is it takes a lot of energy to move a 5000 pond brick down the road at 65mph, if you want better mpg shed about 2000lbs and shape the vehicle like a teardrop.