P1870 code set , need help!!!!

I have a 96 grandam with an automatic tannsmission. The problem first occured when traveling at 65mph in cruise control. The cruise cut off and car seemed to mishift. I pulled car over and restarted and everything was fine with shifting. I have had the car to many mechanics and no one could come up with an answer. The code is cleared but then after 10 miles the check engine light and the ETS off indicator comes on and the code is back. I have recently taken the car to a dealer and they have said that there is something slipping in the transmission and that the transmission will most likely have to be replaced. The transmission shifts fine and has no problems with shifting at all no matter what speed or what gear it is in. Has anyone ever heard of this code and does anyone have any suggestions as to what else can cause this since the transmission shifts perfect and I do not feel like getting ripped off. Any help would be much appreciated.

The code could be a computer issue, or maybe even a fuse. Check your manual and look for any fuses related to the trans. I'm not sure if the 96 has that fuse or not... if the fuse is fine then there may be some type of computer problem whether it's the computer itself or one of the wires from the trans to the computer that could easily set it off.