Vehicle stalls when put into gear

My 91 firebird formula has been sitting for 7 months while I was deployed. When I came home my battery was dead so I charged the battery and the car fired right up with out a problem. I drove it down the street a few times and on the last trip down the street she stalled out on me. Now when I start the car and let it warm up and go to shift it into gear she stalls right out in reverse or drive. I checked plugs wires did oil change. Transmission needed fluid I did that. I replaced the O2 sensor because it was giving me a code and I replaced it and it was really burnt out. There are no more codes and I disconnected the battery and reconnected it and let it run for about 3 hours to get my car to relearn itself but still stalls out once the vehicle is warmed up going into gear.