I would say it is either the TPS or Tune IMO.

Does it (the trans) use a reluctor wheel?

Doug, go get my dad'* kerosene afterburner. It will literally light a fire under your @ss and get your garage toasty in no time. I want to see the T-Bird burn some tires!

I guess you could look at it as a reluctor wheel. The sensor is just a magnet that detects when the shaft rotates based off of the teeth.

Ben, I want that ****ing thing running too..

Is your odometer digital?
Is your VSS mounted in the rear axle?

Just trying to get a better picture of what your setup is, I'm not familiar with your car but it sounds like the eec is thinking the car is going faster than it really is.