Why it take GM so long to learn I will never know. When I bought my Hummer H! with the 6.5 in 2000, I had a conversation with a GM rep at a gathering and asked why not put the Duramax in the Hummer as the 6.5 was such a dog.
He said because the military uses the 6.5. What about the consumer who is paying full boat for the consumer version. Fuel on the 6.5 was about 6 mpg.
The second Hummer I got was the H2, fuels was about 8-10 mpg, a good diesel would have helped both.
Diesels started to get consumer popular way back when prices started to rise, years ago, and its taken them this long!!!
I finally got the Dodge sprinter with the Mercedes diesel, and the worst milage I have ever gotten was 17+ mpg, going 81 mph against the wind. I can't keep my foot out of it long enough to get a best reading, but some say 24+
Europe has gone almost 100% diesel, and here in the US, they just dropped the Jeep Diesel, plus Ca makes it so hard to get approved to bring in diesel for the manufacturer.
The sweetest diesel I ever owned was a 2000 VW bug, yes I said bug. That thing would pass everything on the road, and get 35+ mpg, sold it for what I paid for it after driving it for two years.