Transmission? i was driving down the interstate with cruise control on at 70..the car took off on it's own up to 90 mph. speedometer stopped working and the car shifted to 1st gear and wouldn't shift up. Replaced the speed sensor and it seemed to be all fixed...drove back home down the interstate and did the exact same thing..sped up, speedometer broke, and wouldn't shift up. What could the problem be? Transmission? It is worth fixing?

RFI, radio frequency interference. It has been known to jamb car engine and transmission management control modules which are in fact computers. Mercedes Benz had a very difficult time with this some time back and had to revise the shielding inside their control module housing boxes. That's what this problem sounds like, but if no towers, it's ruled out. At least I believe it to be the ECM, so we'll try a re-set. Remove the negative terminal from the battery, wait a minute or so and re-fit it. This sets all parameters back to factory defaults. Worth a try and we know then there is no spurious data held in the ECM.

RFI, radio frequency interference. It has been known to jamb car engine and transmission management control modules which are in fact computers. Mercedes Benz had a very difficult time with this some time back and had to revise the shielding inside their control module housing boxes. That's what this problem sounds like, but if no towers, it's ruled out. At least I believe it to be the ECM, so we'll try a re-set. Remove the negative terminal from the battery, wait a minute or so and re-fit it. This sets all parameters back to factory defaults. Worth a try and we know then there is no spurious data held in the ECM.