The brakes themselves are probably the same. The difference is that since gas engines generate intake manifold vacuum they generally come with vacuum boost brakes. Diesels have no vacuum to speak of, so the use hydroboost brakes with the power steering pump supplying the pressure. Hydroboost brakes have the potential for much more braking power. On the 6.7 Diesels there is an engine driven vacuum pump, and on some models this is used to run vacuum boost brakes, while other models use hydroboost. I'm not sure if all 6.4's are hydroboost or not. In the past the only way to get hydroboost brakes on a gas engine was to order a dually, but I think that went away with the 2011's.