92 Grand Am, Transmission problems

I have a 92 GA, 4cyl, single overhead cam, automatic trans. I am having issues with shifting. At first it would shift fine, after a few months, it started shifting from 1st to third, then, the other day it took a dump on me. Only 1st gear works and not anything else. I was told that the speed sensor might be the problem, I'm not sure. I do have the service manual for this car, so I will start looking there for answers as well. Any help I would appreciate, thank you.

Unfortunately I think you have a bad transmission. The fact that it will only shift into first indicates that there is a malfunction in the transmission itself. Have it taken to a transmission shop and get it scanned with a trans capable scanner. This will let you know exactly what is going on.