What is are shift solenoid circuit A and B on a Chevy Malibu 2000?

This morning my cars ignition light came on and when i got in to the highway, my rpm stayed constant at 4000 rpm when driving at 55 miles. I took it to a parts store for a free diagnostic and they told me it was shift solenoid circuit A and B. The guys said they were located in the transmission. Is this something i can fix, or something that wont cost a lot to repair? Please dont tell me it means it needs the transmission re-build! Thank You in advance!!!!!!