A personal observation:
When towing with a gas engine and a overall 50 ft length of trailer ......
It's a pain in the A$$ to get into a gas station. Even truck stops can be a pain with 72 Feet of overall length.
Flying J is one of the only stops that have a GAS/DIESEL RV lane.
I still like my 8.1L ..... can run with any diesel through cumberland pass or the notorious Knoxville to Ashville I40 route.
Again ... not that it's better ..... it's personal preference....who knows ..next truck may be the Duramax. Either way, the GM is the most comfortable truck I have ever owned. It is equal in comfort to my Navigator that was traded