1989 v6 auto trans help/diagnosis
 

My wife's 89 4runner v6 auto, was driving with no problems on the highway when the AT Temp light came on briefly and then turned back off. Nothing acted differently, a few minutes later the truck just seemed to go to neutral, and rolled to a stop. No movement in any gear, fluid level correct and new, runs the same, just wont move. Any thoughts? I have a spare trans but am not familiar with the auto trans. Are their codes to check if electrical issue? stumped.