I thought I did, until buying that Pete. Used to drive a lot of vehicles without using the clutch (not always by choice) but keeping track of speed and rpm with an 18-speed was an entirely different experience, with or without the clutch.
It helped a lot when a friend explained what the two little knobbies on the shifter were for (range and splitter) and eventually I got the hang of it.
Anyway, it didn't take long to realize that it can be really tricky to downshift a non-synchro trans once the speed starts getting out of hand. True, the Jake brake helps immensely, but it can only do so much. It became obvious why tractor trailers were going so darn slow down grades - they have to. Using the brakes for controlling the speed really isn't an option, rather a last resort. My driving style has changed for the better since buying that Pete 19 years ago.
Automatics? They generally won't shift, up or down, if the correct parameters aren't met. Consequently, I pull the lever as needed. But obviously within reason, just like you have to do it with a stick.