What your are experiencing is normal. My '91 300-SEL runs about 3400 rpm at 70mph. The 2 shift thing is also ok. These cars by design, start out in 2nd gear. Your shift from 2nd to 3rd and from 3rd to 4th. There's your two shifts.
Enjoy and get use to the high revs. You get power one of two ways: cubic inches or rpms. Your straight 6 ain't got much of the former but plenty of the latter.