1. Client is the Employee to two different S Corps. The person also happens to be a Shareholder. This is Moot to the question. We know this is falls under Business Use of a Personally Owned vehicle. That takes away any Further business perspective for the LLC. By Definition. You cannot Split a vehicle and end up with 100% anywhere else.

2. Meaningless. The person bought a Vehicle. We don't care about their rationalization or justification. We care about Reality. Plans and "meant to" do not apply to Taxes or Reality.

3. Per Reality.

"Even if its not used much is irrelevant, its a business vehicle."

No, it's not. You need to read your own descriptions. Look at item 1 again.

"Should the new truck be used 100% for LLC and other personal vehicle be used for S-corp use"

They should use what needs to be used for getting done what needs to be done. If I bought a truck for the LLC, that means I intend to Carry Stuff. That means I use the Truck for the LLC. It doesn't matter what I use for the S Corps, other than, if I need to haul stuff, I need to use the Truck.

"If i am drastically missing the point and am blatantly overlooking something please advise"

Vehicles are Functional Tools, not tax shelters.

You really are overthinking this.