Super Duty gets a 10 speed and an updated diesel

A flat torque curve means as the engine slows down as a truck is pulling up a hill the torque remains the same at the rear wheels... you feel the same push from the seat throughout the entire rpm range that the torque is flat. It also means the the power at the rear wheels is dropping off as the engine slows down. As the engine rpm drops a downshift would keep the axle turning the same speed but cause an increase in torque and therefore put more power to the rear wheels. More gears allows the engine to run slower when less power is needed and higher when more power is needed. The ten speed should help obtain a little better fuel economy as well as a greater pulling capacity. On the other hand the new diesels, especially the Cummins have a fairly flat power curve, ie the torque builds as the engine slows down. This means more gears is of less value as far as pulling goes. My Peterbilt has an 18 speed transmission and a completely flat horsepower curve. At any one speed I can select one of 3 different gears to run in. Running in any of the 3 gears will put exactly the same power to the rear wheels.