"You keep stating that because a truck is present it will be used for all things."

I keep asking why in the world would anyone be advised not to use a Truck they own, when the truck is Owned, and a Truck would be used? What tax regulation tells us it is Advantageous to buy a Truck and not use it? How does tax guidance change my use of Vehicles I bought intending to use as vehicles are used? And if the LLC "owns" the Truck, that is the same as Personal. So, this point is Moot. The only real separation is if a corporation owns that vehicle.

For this: "Your basically saying no sole owner or owners of a business can possibly say their "business" vehicle is used 100% for business, that doesn't make sense."

I teach the word Discoverable. As in, if you turned in mileage for that same vehicle to each S Corp, there is no possible way the LLC has it also as 100%, because this is Discoverable = entries were made and reimbursements for mileage were made. Proof is required under An Accountable Plan. Once you provide that Proof, it's sort of hard to also state otherwise, elsewhere.