A bloke on reddit revealed what appears to be the "slate auto" prototype truck. It is likely nothing other than a shell with wheels, which is common for first prototypes (the bmw i3 did this, and many others). I found it through the autopian which is an excellent publication.
I can't help but notice the striking similarity to the Comanche. The slightly larger cab bump. The front rectangular grill with the side lights. The incredibly boxy and simple design. More importantly:
Stellantis, wake up someone's going to out Jeep you!