I am not trying to disagree with you about the SUV Hybrid's gas mileage, but this website says otherwise.
http://www.fueleconomy.gov/Feg/findacar.htm
If you look up Chevy Tahoe hybrid, it only gets 21 city and 22 highway. Not much better than the regular non hybrid version. But that is just one website. When I went to Chevrolet's website, I couldn't even find where they post the info about the MPG on their Hybrid SUVs. But I thought I even remember looking at the MPG sticker when I was last at a Chevy dealership last year and thats what the sticker said, somewhere near 21 city and 22 highway. But like I said, this is only one website, so I could be wrong.