First: a trans oil and filter change is a good thing every 30,000 miles. Make sure you drain the torque converter too. Second: a Mercedes trans does not shift like a Lincoln or Cadilac where they shift smooth and glide from one gear to another. My Mercedes 93 190e will sometimes "bang" into the next gear under normal acceleration. When I say "bang" lets just say its a very positive shift. Its not always but its a trait of the car.Third: as far about playing with the shifter... don't. If the car drives fine in D and 3, then leave it alone. The only time I use 3 is accelerating by shifting from d to 3 so I dont have to use passing gear by mashing the gas pedal to the floor. I also leave it in 3 if I'm on a back road where I don't go much over 45 mph.