This is like talking about a 2 cycle vs 4 cycle. Which one will climb the mountain first. The gas engine will climb a hill the same or maybe a little faster or slower.
The difference is what rpm will it take for either one to climb that hill. Lets take a 6% grade. The gas will climb this hill at 6,000 rpms, the diesel will climb at 2,200 rpms.
In this situation the diesel is not burning as much fuel and the engine is not working all that hard, where as, the gas engine is almost red line and sucking up all kinds of fuel. This is the difference. Not which one will climb faster or not.
1997 Triple E Empress, Freightliner Chassis, CAT 3126 w/ 275 horse's.
MD 3600 Tranny, 2011 Ford Escape Hybrid w/Blue Ox tow bar and Roadmaster Base Plate.
Amsoil Synthetic Oil only for my baby.