Saturn Transmisson Problem?

I have a 2000 Saturn Ls.. I was driving it one day and it began to Jerking, my speed decrease, and my speedometer needle was jumping up and down. I took my car to Amcco and they told me it was sensors. I have change all speed sensor, including the wheel sensor because my car does not have Abs. Now my car is stuck in first gear, speedometer needle will not move and I don't know if its an electrical problem or if I should replace my transmission?