You could always call the cops and they can run the plate. They should b able to tell you who the truck is registered to, thus they find the company, and then the guy get's his ass fired! Problem solved.
I was driving along the interstate today, and I went to pass this truck. Well, the truck driver for some unknown reason started to get aggressive and dangerous. I was able to get his plate number and his state, but not the company of the truck. What should I do?
Answer to main question: Stay out of his way. Your not going to "do" anything. It's his word against yours even if you managed to get anyone to follow up on it. And that's not likely.
Call Highway Patrol & have them make out a report.
Be sure to give them accurate info on the time of day & date, so if necessary, they can figure out who was driving the truck when that occurred. Your single report may not lead to much, but when enough people report that driver, they may take a serious look at them.
http://watchtower.org/e/200802/article_01.htm