Whatever you do, don't 'brake check' them. You have some idiots driving big trucks.
Make sure your speed isn't fluctuating. I get stuck behind a lot of cars on the highway who will slow down to 50-55 mph on a 70 mph highway, and only speed up when somebody tries to pass them. (only to slow down again)
If the truck is tailgating you. the smartest thing to do is get out of their way. They'll kill you. Get a truck number, call the highway patrol, with a description of the truck.
(Color, make, truck number, type of trailer, direction, etc)
Don't bother to call the trucking company. You'll get the run-around.
The police may not do anything, either, but chances are good if they pull that truck over, they can find something else to ticket him for.
Of course, a rear facing dash cam is your best option.
If areas with long downgrades, which are usually marked to warn trucks, and usually they have a reduced speed, keep away from the trucks!
Even with 'bad' brakes you can slow down or stop a truck, but many truckers have no skills or sense.
The smoke (and smell) you'll see coming off of the brakes on some trucks on a long downhill is from the brakes not being adjusted correctly. One or more brakes has to do more work than the others, overheats, and smokes. They will catch on fire at times, but that isn't fatal in itself.
Park, let the fire die, cool the brakes off, ADJUST THEM, and you are fine. (Assuming the flames weren't so big they melted air lines)
The worst 'runaway' truck accidents happen when the truck not only has brake problems, but the driver panics and gets caught out of gear. Nothing between you and the laws of physics to slow you down.