Help
 

I have a Mercury Sable 1998, low mileage only 73,000km. It has on occasion mostly when I have had on the highway but just did it in city at 80k, all of a sudden the speedometor drops, the rpms show that they rev right up to 4. Unable to get much speed ,hesitating etc. Garage people said might be speed sensor. Cost enough to replace that and then they said still won t be sure to fix it. Anyone have this problem maybe I can fast track a solution???? Someone else told me to change the tranny oil, I had a fall check they didn t mention anything wrong with the tranny oil.
thanks

Is the check engine/ service engine light on? If so, have the codes read and post the EXAACT code number back here. If the speedometer is dropping to zero, there should be a code stored in the computer.