You are always a volcano of new ideas !!!
I have a question (one of my usual slightly embarrassing questions...)
I remember you had built a model of a bulldozer that had collision meches in the shovel and could load and move objects in a very realistic way.
Do you think it would be possible to equip a robotic arm with collision meches such that it would be possible to "grab" an object from the ground, lift it and unload it into the flatbed of a cargo vehicle like the Landrock Tributary 3500 XL you're talking about?
If it seems to you that the idea is feasible (and you have the desire and the time to try)
I have found a model of a robotic arm in "obj format" for free use
https://www.cadnav.com/3d-models/model-41371.htmlit has only a limited gripper travel which, however, can be easily enlarged in Blender.
You could mount it on the back of one of the many free models of vehicles found on the Web and go around loading and unloading goods.
It's just an idea...
It would be nice if it was achievable ...