I haven't dealt with any brand new trucks like you're considering, but I do know a few years ago when the shop I worked at was putting EGR/DPF Delete kits and Emissions delete programmers on the early 6.7 trucks most people claimed they were getting 10-12 mpg empty. Once they removed the emissions programming and compenents it jumped back up into the 16-18 range most Cummins owners are used to. If the new ones are still in that same range then I don't see how you could justify spending the money over a gasser that will probably pull the same mileage.