It has been mistaken as many different things:
Torque Converter shudder is usually not the first guess that mechanics and non-mechanics will make when this symptom first surfaces.
What you usually experience is a slight shake or vibration in third or fourth gear that is downright annoying. It has a certain "washboard road" feel in the seat of your pants. Drivers usually just live with this problem until they can't stand it anymore.
Torque converter shudder is very simply caused by worn-out transmission fluid. The lock-up clutch inside the torque converter is slipping/grabbing giving the shudder effect.
The fluid is originally died pink at the factory so you can tell when the fluid is failing or oxidizing. It will turn dark red, then change to brown, and finally to black. Automatic transmissions are designed to slip as part of their normal operation. Poor quality fluid allows too much slip and eventually causes failure. In severe-duty vehicles like Police, Limo, Taxi, the fluid quality is much more crucial.
Use an Automatic Transmission Fluid Exchanger/Flusher to completely remove the old fluid every 20,000 miles (severe-duty). This process ensures that the fluid is reset to 100% performance efficiency. The torque converter lock-up clutch will no longer chatter.