Mercedes Benz repair: 1989 300SE transmission, auto tranny, tranny fluid

Question
On my 300SE I only count three gears and at 65 mph the rpm is 3200. I dont do much hiway driving so I believe this car has been like this for some time. Otherwise tranny performs excellent. Where should I start checking? I believe this has a 4-speed auto tranny.

Answer
could be a number of things, i would first flush the tranny witha new filter and the torque convertor, refill; it with proper mb tranny fluid, and see if it shifts differently otherwise you would probably need to replace your k3 spring in your tranny pretty simple go to benzworld.org and do a search on replacing k1 spring then youll have a understanding of the mb tranny