Mules are slightly smaller than their horse parent, and when they grow they share traits of both a donkey (the long ears), and the horse (color, tail, etc.). A Mule in the grass.
For example, a 2014 Ford F-150 is considered a half ton truck but most variants can carry a lot more than 1,000 pounds in the bed. Since these terms are probably not going away any time soon, it's best just to think of them as smaller, mediumest, and more than medium.. (Pause for laughter).
Yes, that's very overweight. Most half ton trucks aren't rated for more than 2000lbs of bed weight. You will have the same issues mentioned above for too much tongue weight, most notably fried suspension. They call it a 1/2 ton truck.