wild guess: If the transmission shifts fine and only jerks around when the torque converter lockout is operated (this thing only works in 3rd and 4th gear), you most probably have a problem with the torque converter lockup. This thing is controlled by solenoid switches that might be faulty.
Unfortunatlely, I don`t have any idea how to fix this except take it to ZF (the transmission is made by ZF). Look up their service network here: http://www.zf.com/defaultz.asp?lang=1&id=1166.

I`m glad to own a 6-speed manual version - clutch replacements every 300 k km and that`s all....