Well I recently had a 96 Sbale that did the same issue. It would kick/Jerk into 1st-2nd gear. Come to find out the tranny was leaking fluid due to a metal bar on the inner most part of the car when you open the hood. If your car has that metal pipe on the bottom check it to see if it is leaking tranny fluid by starting the car and watching it. Otherwise if that is not it then take it to a garage and have them check the sensor and tranny.
The Input Speed Sensor, AKA Transmission Input SPeed Sensor, sends a varying frequency signal to the TCU to determine the current rotational speed of the input shaft or torque converter
. The TCU uses the input shaft speed to determine slippage across the torque converter and potentially to determine the rate of slippage across the bands and clutches
. This information is vital to regulate the application of the torque converter lock-up clutch smoothly and effectively.