Don't play policeman. Don't try to make a truck driver conform to a bureaucrat's idea of what is right and wrong on the highway. As an example, Taylor cited the way truck drivers handle hilly terrain on the Interstate. A fully-loaded truck slows way down going up a hill. On the way down the other side of the hill, a fully-loaded truck gathers speed quickly.
Truckers like to use that speed to help the truck up the next hill.
Do not sit in the passing lane going the speed limit. Let the truck driver pass, and let the Highway Patrol worry about citing the trucker for breaking the law. No assistance in lane changes or merges. If a trucker has his turn signal blinking, leave room for the truck to merge or change lanes. Indicate your willingness to allow the truck in by flashing your lights.