I haven't read eyery post here, but wanted to add that I think Hummer owners take a bad rap.
I live in Texas, where every third or so vehicle is a truck - and not just a regular truck, but a Dodge Doulie 4WD ( that gets 12 MPG tops ! )
I assume the reason Hummers have this bad image is that they are an
icon which represents greed.
As far as the mods that you could make to your H2 right now, you could remove the roof rack and block off the grill ( free MPG all you need is a wrench and some coroplast for the grill -you could even put it behind the grill so it doesn't cover up your front end and look funny ! ) ( These could add 2 mpg ..or more )
You can also lower the vehicle and add a flat underbelly.
You could pick up around 3mpg ...and it will lower the center of gravity on the thing which will make a rollover less likely ( it will handle better )
And it will look pimpin too
The above aero changes would mostly work when at highway speeds.
Around town, you'll want to lighten that monster as much as possible.
Leave the spare tire and tools at home - when was the last time you had a flat .... really.
You could also have your gears changed to something more highway friendly - that would help a lot I would think.
Slowing down tp granny speed will have the greatest ( positive ) impact on your MPG.
As far as making the H2 more Enviro friendly, there is not much you can do besides an engine swap .... which is something you might actually really like.
MTV's "Pimp My Ride" recently had '65 Impalla that had a Duramax ( Diesel ) V8 transplant. The motor pumped out over 800 H.P. if I remember correctly ( it blew away a Lamo in the 1/4 th ) ......yet it was powered by clean burning vegetable oil ( BioDiesel ) ....................and the best part ........it got
over 20 MPG ! This is in a car that probably weighed in at close to what you are driving now.
An engine swap would be pretty easy with your set up too, since you already have a monster size engine bay for it. You could even sell the current motor to pay for the transplant.
Bio diesel is clean, domestic ... and it smells like french fries too ( Hey that's a
good thing
Who actually like the smell of regular Diesel ?? )
You don't have to worry that you will be stranded if no bio is available - you can fill up with regular diesel just as easy.
Clean power, doubling your gas mileage, having power out the wazoo ... it's a win / win situation ... and you get to keep the toy !
Good luck !
Edit : One more thing : UC Davis has a suburban that is the one that the Hummer is built on - so basically the same vehicle.
It gets 25 MPG.
How ? The
students converted it to a hybrid
http://www.team-fate.net/sequoia.html
It now has a 70 mile all electric range, 0-60 speed of 9.3 seconds and a top speed of 99 Mph