1997 Chevy Lumina Service engine light on and transmission

Drove to work every thing running great.
started home, hard and slow pulling off from a stand still odomiter not registering. Service engine light on for the first time.
Stoped, chedked transmission fluid which was down to add line. Added fluid then started driving, for first two miles was slugish holding in low gear longer then shifting. After about two miles the odomiter started registering and driving normally, Service engine light still on. Running normal. Let sit while at a meeting for over an hour, the same slugish and odomiter not working for two to three blocks. Ther are no leaks under the car. What are the possibilities?