Reasons why diesel engines are far superior to gasoline engines.
Far more torque. A typical gasoline engine has a torque to horsepower ratio of something like 0.9 : 1. A diesel on the other hand is more like 2.5 : 1 or even higher. Why is torque so important? Well, torque is what actually supplies the power to move the vehicle and anything you might be towing. Horsepower tells you how "quickly" you can apply that torque to the ground. A big rig might only have a 400 HP engine, but it also puts out 2000+ pound feet of torque. That's why a big rig goes up steep hills so slowly when he's loaded, but he can do that forever. If a big rig had a gas engine in it, he would slow down much sooner, and he would likely not even be able to make it up a really steep hill, because he would simply not have near enough torque to pull himself up the hill.

Not to pile on, but when I read this from the DG site ^^^ last Sunday night - something doesn't sound right about the torque pulling a big rig up a hill at speed - versus the horsepower that is doing the work. Is the above explanation of torque vs. horsepower, correctly applied physics?