3,000 RPM at 70 MPH is about right. Your car has a 4 speed hydraulic
(4th is a 1:1 ratio), as opposed to the newer 5 speed electronic boxes
(5th is an overdrive ratio); the engine then runs at 2,500 RPM at 70
If the transmission has a dip stick have its fluid and filter changed
every 30K miles.
MBUSA will send you a maintenance schedule for your car.