The Hummer brand, like all other Tactical Military vehicles, is designed to get from point A to point B, through whatever terrain it needs to get through.

Show me one Military vehicle that is fast, or has a low rpm passing gear?
There are none.

4700lbs, is heavy. Not as heavy as other vehicles, but heavy non the less.
220 hp, is more than ample for the 3, to get it where it needs to be.

Want something faster, or more powerful?

By a V8 something or other.