I have an automatic 1989 240 dl. Yesterday I noticed that the speedometer is acting up. When I am idling, my car is now really shaky and the speedometer bounces around between zero and 10-ish.. Then as I start to accelerate it moves normally until I hit about 20 mph and shifts up.. From there, the speedometer does this weird jumping thing-- not up and down but instead of moving smoothly it jumps up about 5 mph every time. It's stressing me out and I just got a new transmission about 2 years ago so I'm hoping that isn't the issue.. Any thoughts or advice would be greatly appreciated.

 

..."really shaky" most likely indicates an engine misfire. I'd address that first, the speedo jumping may be as a result of that shaky engine, not too clear there on the description.
What are the chances of a missfire and a speedo fault suddenly happening at the same time?