I would gear down with the gasser and carry on and apply the same torque to the drive wheels. The mileage is no advantage given the extra price of fuel and service to a post 2011 EPA diesel. Sure if was like the old days of the late 19980's here when we had carburators, much cheaper diesel fuel and simple diesel engines, then sure. It's 2014 and the vehicle hating pricks in the EPA are busy legislating trying to find ways to outlaw diesels on CO2 . When engine manufactures managed to meet emissions specs the EPA had thought impossible. Now you have to service a 30,000psi common rail injection system. A variable waste gate on the turbo. A cat convertor. A particulate filter. An urea injection system. Replace two batteries and two alternators on some vehicles. Glow plugs. Gelling fuel in the winter time. There was a time when the diesel ruled but no more. A DI gasser is the simple reliable engine now that goes 300,000 miles with just plugs, belts and filters.