From your recent photos I was able to discern that the spare tire is 'exposed' to the airstream, where I had presumed that that portion of the belly were perfectly 'smooth.'
We know from Subaru wind tunnel testing that this is 'lethal' to 'aerodynamics'.' I've been unable to find a technical drawing, showing the underbody in detail. The local GMC dealership says they can't get 'anything' about your ZEVO out of GM. They all saw it at a GM clinic that they attended in Kansas City, but they haven't heard a word about it since.
The RIVIAN-built Amazon-Prime delivery van may have sent everyone else back to the 'drawing board'.
