Buying a new truck

We've been crazy blessed with our 2004 Duramax dually over the years. It consistently gets 15.1 mpg highway empty and no tailwind down to 15 loaded with camper mountains or flat not towing. Haven't towed anything with camper on but will this spring. However is only a one horse tandem axle and boat is just a small 10x5' John boat. Still pretty good mileage. We have, over the years, done some front end work, injectors, and a VSS module replacement but that's it. Very fortunate. It had always been a work truck till this past June, when we picked up the camper, hauling Masonry tools, scaffolding, tractor, bricks, blocks and cement. Not exactly a sheltered life. Like I said we've been blessed with a really good truck. Hopefully it will last well past it's now current 170,000 miles. We get it serviced more frequently than recommended and if it squeaks, or leaks it gets fixed Pronto.