So for $39,000, a Hummer H2 owner can get a Duramax diesel/Allison transmission (see the blue Hummer) swap and increase fuel economy up to 22mpg.

A 2003 Hummer H2 is listed for $19,800, but this is a modified example with 133,000 miles on the odometer. Stock examples are less common, but an example of the 2008 model year with 129,000 miles ...