1986 GT starts, then stalls in gear

1986 GT auto- Anyone have this problem? Starts fine, and can shift straight to neutral no problem. When put into gear will stall instantly. Was (is) prob low on trans fluid. Will topping that off help if the torque converter is locked up? Have heard the IAC could need clean or replace, trans shift solenoid bad or maybe the the park neutral switch bad? Any suggestions?