transmission problems

[mischa]

TRANSMISSION PROBLEM
I recently purchased a MB 190 E 2.6 Automatic 1991 and because i was first in the city driving I did not realised that the 4th gear is "missing".
When I am on the Hwy the rpm's are for 100 km/h 3000 which is I think about 1000 rpm's to high,the engine is rewing and of course the oil and gasoline consumpchion is higher then it is suposed to be.
Also I realised that the spedometer is not working properly,it is showing higher speed then it is realy,for example if I drive 100km/h it show's me 120km/h,plus the traveled kilometers I usualy go from work and to work is also higher then it is realy,for example with my another car the distance was 32 km but now the distance on the mercedes shows me 41 km.
If anybody know what could be the problem please give me some advise maybe I can fixed on my own or in worst case I have to go to dealership.


P.S.
Do anybody know is it possible to put a manuel 5 speed in this car and if it is where can I find these parts?
190E 2.6 1991