im a class A driver meaning i have a CDL and as far as the double clutch thing, you do not need to use the clutch to shift from gear to gear only on take off, can you imagine what your leg would feel like if you double clutch all day in a twelve speed... for a noob to driving trucks you might need to double clutch in a commercial transmission when you push in the clutch it actually stops the trans from spinning its called a clutch brake for the people who have not yet learned the sweet spot of the trans to shift without a clutch, the only time a driver might use the clutch to shift gears is when they are overloaded with weight but even then double clutching is not needed. they teach you that in truck driving school that you need to double clutch but i do not know anyone who does it in my line of work in a commercial vehicle it is a waste of time and actually slows you down.