Couple things here
1) the chevy was not a diesel. You can see that there is no Duramax emblem on it. and the exhaust is not the diesel exhaust.
2) the cummins was programmed, you can tell by the black smoke (rolling coal)
So what we have here is is a programmed cummings pulling a 6.0 liter GM.
Not really that impressive
However, Im betting that the guy in the Chevy kept running his mouth about his gas engine out pulling the cummings. Might explain why the guy in the cummins took him for such a long ride. Not only proved his point, but made it hard to ever forget.