What is the right course of action?

On German Autobahns, the "keep-right" rule (Rechtsfahrgebot) requires drivers to use the right lane whenever possible, except when overtaking. In the scenario described, you are overtaking a long line of trucks in the right lane, so it is correct to reduce your speed slightly and stay in the middle lane if moving to the right lane would mean constantly changing lanes between slower vehicles. This ensures smoother traffic flow and maintains safety during a prolonged overtaking maneuver. However, once you have finished overtaking and the right lane is clear, you must return to the right lane as soon as it is safe to do so. The key point is: only use the left or middle lanes for overtaking or when the right lane is unsuitable, and always return to the right when possible. Your selected answer matches this rule.