I have just bought my first mercedes....it is a 1990 350sdl, I am wondering what rpm's I should see on the tach at 60mph...I am registering around 2500, which seems a little high to me, I am assuming it has a 4 speed automatic transmission as I can feel 3 shifts, but I cannot detect any lock up on the torque converter, is this normal? I am accustomed to american vehicles.

2500 is normal for that car. The torque converter does not lock.