The Duramax is on the way back to GM as a repurchase. However, we used it to pick up the replacement Powerstroke. Here's our fuel mileage on the way back home.

Both trucks are 4x4 turbo diesels with 10-speed automatic transmissions.

TLDR; Duramax wins by a large margin but, I'm not upset with the Ford though. 1050ft-lbs is a lot of muscle to feed.