2500 RPM Surge on 2000 Ford Windstar

While driving 50-60mph my tach reads 2000 RPM then spins up to 2500 RPM vehicle surges or hesitates then some what smoothes out. I have changed spark plugs,wires and fuel filter. Any Ideas?

Asked by for the 2000 Ford Windstar
Yes, it may be the Torque Converter Clutch is releasing and applying, so it feel like the car is going from over drive to drive to overdrive etc.

Any Service Engine Soon Lights coming on? If so, get those codes pulled!
A trans code will be a P07xx type of code format.