Heater, Drive Shaft

Hi
I have 300D 84, and i feel a lot of viberation underneath the car ( between the front seats) when accerelating from zero real fast but it goes away after reaching normal speed, i though it might be the rubber mount for the intermediat shaft or may be the ball bearing, what do you think,I also have a problem with the heater( weak heat in idal, good heat between 10 to 40 miels and then very week heat over 50 miels on the highway),i tried to test the monovalv by dissconecting the elctrical plug that goes in it and though that this will set it to max heat all the times but it stil acts the same thank you very much for your help.