my buick against the truck. IF there was no escape it seems to be the only way to scare him into backing off.
It comes down to weapon, intent, delivery system.
Did they have a weapon? Yes, the truck could serve as a weapon
Intent? The intent is iffy. There intent as far as I could tell was they wanted to drive as fast as you would allow. Believe it or not some drivers are just bad and they think they are ok if they follow you on your bumper. Since they think "well I have control of the throttle, and I wont hit them" they think they are ok. However to the person they are following its a completely different story. Again if the person had rammed your car, swerved in a manner to push you off the road (more so then in a case where they might not have seen you in their mirror) or something like that, you have intent. In the case posted the intent to cause you great bodily harm or death just isn't there. Its more of a case of bad driving on the truck drivers part.
Delivery system: The semi when used in a manner to put you off the road the delivery system.
We know the situation doesn't warrant the use of deadly force. However the displaying of force to end the situation can be appropriate. If a gun is the only option you have, and you can’t slow down/take a exit/speed up/escape the situation, then its better then nothing. However flashing a gun in that manner might not be legal per your states laws. Calling 911 on a cell phone and having the police show up will be a good thing to do. Since your not in a squad car, and you have your family to think of, its unsafe to try to take matters into your own hands in that situation.
I have been in the same situation as you except I was being tailgaited by a semi in a 1 lane construction zone. I really was afraid if I put on the brakes at all I was going to be run over. What I ended up doing is bailing on the next available exit. Even if the person was trying to ram me I would have tried to speed up as fast as I could rather then try to get a shot out to stop the driver had I been armed at the time. At high speeds and under stress the last thing you need to be worrying about is shooting behind you at such a small target. The semi has you beat, your car wont stand up to it, and odds of getting a shot that stops the threat is slim. Even displaying a gun isn’t likely to do much since the person might not even see it. Even if they do who knows how they will react. Its better to get the hell out of dodge if at all possible.