I am also an engineer with similar truck needs and driving habits. Have you test driven a 2020 Duramax yet? If not do so, the first push on the accelerator will likely make you forget about cost analysis. When you hook up that 8k camper the engine/transmission will have @ 70 before you even think about it. I was in a Siverado 1500 with 5.3 liter and needed a truck with more weight to stabilize my camper towing and I always felt the smaller truck was being abused when I towed our 8k camper. I haven't made my first payment on the 2020 Silervado 2500 Duramax/Allison 10 sp and maybe my mind will be changed when I do, but the torque and smooth shifting of this combination is likely to make you forget about fuel costs, def cost, 10 quart oil change cost and anything else. You will give up a little ride comfort in a heavier truck for your every day drives, but it will give you a bit of piece of mind when towing.