jerky shift please help

My alero jerks when shifting from park to drive or reverse. This just happened recently after the security system would not allow me to start the car. I disconnected the battery and then reconnected it and put the key on the on position for 10 minutes. The car started but by jerky shifts began. When the check engine light is off it shifts fine, but when it is on it is jerky. The light rarely stays off and normally goes on after I back out and shift to drive. Does this appear to be a transmission problem, sensor problem both or something else? Please advise. Sorry I forgot to mention 2001 year and v6 3.4 engine.

Helpful to post year, engine size and mileage.

When the SES/CEL light is on get it scanned for odb-ii DTC error codes.