Yep, that's the J-Gate! The left shift path is used for manually changing the gears and it goes through the "D" mode, on 1st gear, naturally.
To still remind of the driver that it's the "D" the manual mode is only passing through. What is the Spicer Truck???
Oh wow, I love hearing about these super weird things Truth is, it's just a mockup of something that I imagined would be as unrealistically complex as you can get (excluding circular paths), but as usual the stupidly complex thing actually exists... Here's the original drawing of what I asked for And yea, it's "just" a testing prop, we do these sometimes for implementing new systems. Very helpful Video - Click to Play - Direct Link
Do you actually have any legit source saying its a 20 speed spicer? those were usually twin sticks with 6x4 pattern, and if not, it would be single stick with range selector on the shifter I've seen the image you've posted many, many times on the internet, but theres very little chance something like that could even work linkages wise on a mechanical transmission. I could see something somewhat similar happening on hydro drive mining truck or a buldozer, but even then, not to that extent
There is already a T-Series mod that lets you run Twin stick as well as 18 speed, with multiple shift patterns no less
As far as I know the shifter pattern itself is an old joke, people just refer to it as "the Spicer 20 speed" in jest.