Cadillac Repair: 1995 Cadillac Seville STS, cadillac seville, throttle body

Question
Going at high speeds, (like around 50 or 60 MPH) the RPMs will suddenly drop and then shoot up to almost 5000 RPMs all the while the gas pedal is in the same spot, and during this time ( which is about 10 seconds) the car will jerk back and forth as if I am pressing the break repeatedly but will then suddenly stop. occationaly it feels as if the transmission wont shift, but it corrects itself. also the speedometer only works sometimes, i think the problem is related to the throttle body but i am not sure, what is the real problem?

Answer
IS or HAS the CHECK ENGINE light ever illuminated while driving the vehicle and or has any other lights illuminated or any messages from the message display center ?.

What work or diagnostics of ANYKIND WHAT-SO-EVER have been performed on the vehicle trying to fix this problem ?.