1991 Accord Transmission or computer problem?

My green "S" light has been flashing on and off for a few days. When driving at high speeds the car would feel like it would hesitate for a fraction of a second and then go back to normal. Just now, as I went out to start it, the shift was stuck in park. I had to use the shift release key lock to get it into neutral and then start it. Now it is slow to accelerate, but does drive.

The flashing green light and hesitation happened last fall also, but went away until now.

Could this be the little computer that tells the car when to shift gears, or do I have an all-out transmission problem? I read last fall that there is a box with the computer in it somewhere under the passenger side seat and that the problem was probably with that.

Thanks for any responses.