They should handle the load about the same in the same truck. The only difference is the weight of the truck. A heaver TV handles a trailer better. Also a longer truck handles a trailer better. But just between engines, you will be happier with the diesel. Company I used to work for had a 05 Dually 6.0 Gas job, and a 06 Dually with a LBZ. Pulling the same trailers with the same weight on them, the 6.0 was lucky to see 5 mpgs, while the LBZ saw 12-13. Plus with the LBZ, you would forget its back there. They both pulled the same from what I heard. Never drove the gas job, the engine blew up at around 125K miles, while the Duramax had twice that and is still running strong. They were usually around 35K GCVW all day. I am reminded everyday why I bought a Duramax, the 6.0 Chevy I have at work feels like its trying to pull the moon with just a little single axle 3K pump behind it.
I will never go back to a gas truck or one with out training wheels
