1991 Mercedes 300 e 3.0

[jcoinc]

Hello,
I am a bit new at this. I bought a 1991 300 e sedan with a 3.0 engine. The transmission was bad. I had a rebuilt trans installed. The car shifts great in all four gears. My question is there an overdrive? When I am at 60 mph the tach is reading 2500 rpm. I have a 1994 Chevy Camaro and at 60 mph it is about 1700 rpm. Just making sure this is correct.
The next question is that the cruise control will not hold. I have it on and push up on the set lever and it engages for about a minute then shuts off.
If some one can answer these questions it would be deeply appreciated.
Thanks