Economic driving destroys engine???

Hello, I drive a truck this week, Actros MP2 1841(sattel) This vehicle is extremely Economically moved with a, Fleetboard value of 9.6! so always switched at the latest at 1600 turns. Now I got in and thought to myself what’s going on? The engine no longer comes over 1600 turns, and then it takes forever until it comes to 1800-1900 turns. It seems to me as if someone holds it and doesn’t let it go. (That’s even if you’re alone with the SZM is driving). Can it come from the fact that the engine has no rotational speeds of more than 1600 revolutions?