My wife has a 1999 Legacy Wagon, 4-cyl. with 80K. When it has been driven at least 15 minutes, within a period of no more than a half second, the speedometer and tachometer needles will drop to about half and return to their original setting, the AT TEMP light will come on and the car will jerk as if it momentarily shifted or tried to shift gears. It returns to normal (light goes off), but will continue repeat the above on a random basis from a few seconds apart to a few minutes apart.
If you shift to third, the light blinks on and the speedometer drops, but the tach doesn't move and the car does not jerk.
If you are running cruise control and it does the above, it turns off cruise control.
We've had the fluid changed and 2 of 3 speed sensors replace with no change. My mechanic says the remaining speed sensor is located at the top of the transmission and would require dropping trans. He's not hopeful that would fix the problem. Any ideas?