what does the code P0770

Question

My car has been showing this code for about 6 months now. But yesterday we were driving for about 45 minutes on the highway, and it stopped accelerating. This is the only code that has ever popped up. We dumped the transmission fluid once we got home, and it worked for about 10 minutes, then it stopped accelerating again. Can I replace the shift solenoid e and fix this problem, or is it more then that?