Two Pickups with more similarities, such as the body structure, starting price, ground shadow size, height, and maximum occupancy, than differences, like the powertrain, horsepower, and fuel economy. First of all, the 2018 Ram 2500 Mega Cab has bigger and thirstier engine; the 2018 Nissan Titan XD Crew Cab Diesel gets 2.5 more mpg. Among similarities are the body structure, starting price, ground shadow size, height, and maximum occupancy.