My LBZ when it was still stock ate up all 3 modified Dodge/cummins I raced
A friend has a 2013 Dodge/cummins and gets 10 to 11 mpg always even towing
THe worst thing about having the Duramax/Allison emblem on your door is that No One wants to race U

 

I second that

As stated earlier though. There both diesels, so you really can't go wrong. Intended use is your best deciding factor.

 

I had an 05cummins and my current 06 LBZ, and you couldn't straight up trade me for a cummins now, I'll keep my LBZ, its quick, quieter, smoother riding, pulls a trailer like its not there, has 6 gears in an auto, shifts nice, and the interior is better(nicer seats)

I liked my cummins, I love my Duramax, and my mileage was the same between trucks, virtually no difference at all, both trucks tuned