Even at a safe following distance, the already moving air behind a truck lowers your effective speed by 20mph or so, saving 25-50% of the fuel bill. Trucks that have very little ground clearance (eg a big mudguard across the back) work best.
In the extreme case, in an EV, you can end a journey with more battery than you started with if you follow a truck closely (rather too close for safety, and in perfect conditions)
The effect of drafting though is incredible. If you're ever able to get behind a big truck on a bike, it basically becomes effortless to get up to 30mph and stay there. It's quite a thrill (just make sure you have an escape route)
Please either back those numbers up with evidence or remove them for the sake of road safety.
Obviously it's unsafe to do on the public road for a bunch of reasons, but it really shows how good automated vehicle convoys could be for the environment if they can get close enough.
Here is a video of the effects of the same airflow: https://youtu.be/xkbe2NP30Fs
They estimate the savings at insane 20 feet at 20 something. Far from your claimed 100%.
Could it be, that your road is not as flat as you think? That would also explain the necessary braking to not run into the truck, wouldn't it?
But I couldn't agree more: let the machines do that perfectly and safe. Let's reap those sweet 25-50% increase in fuel efficiency.