Your speedo wouldnt show a bad reading if the sensor was doi g its job. The speed sensor is connected directly to the cluster, the cluster sends the vss signal to the tcu. The 1st thing id check firs would be the yellow/green wire between pin17 of the cluster and pin 27 of the tcu, that the main signal wire. Theres only 1 speed sensor in the tail of the trans, but theres a engine rev sensor on the top left of the trans that could vauae it to go in fail safe.
......And just as they're about to catch me.....Twin......Turbos......Kick.......In!