Detroit claims that would be impossible. But they whine every time something new comes along. They whined about seatbelts and other safety requirements, saying that it would be too expensive.
Now here is a guy who is actually making Hummers get 60MPG with twice the horsepower of the stock models. Read about the Motorhead Messiah. He is doing some amazing things.
And of course the article also points out what a piece of crap the Hummer is anyway as his new stock Hummer required repair three times on his 200 mile trip home from the showroom floor.