Both cummins, not apples to apples. Mine is 2013, his 2012. He is towing more weight, but is also tuned with 5" exhaust. On the big hills if I don't manually shift from 6th to 5th he will start to catch up to me until my truck shifts. Then I start to regain speed and his starts to fall off a bit until his shifts, if it does at all. If I manually shift before cruise let's it lose 3-5 mph before shifting down I walk away from his truck until his shifts because he is letting his shift on its own and losing those 3-5 mph before shifting.
Empty, my all stock 2013 nets 3-4mpg better.
