Q: Engine stalls when put into gear

Hello. Engine stalling can be caused by a wide variety of issues. Anything from transmission issues, fuel problems, to wiring problems can all cause an engine to stall when put into gear. If you recently rebuilt the transmission it may be possible that the issue is related to the service. As you stated, it may be possible that the torque converter is locking up for some reason, perhaps due to a mechanical issue or a fluid pressure issue. It may also be possible that the stalling is being caused by issues with the engine management system. Perhaps an issue with one of the components, such as the fuel pump or idle air control valve is causing the vehicle to stall out when put under load. I would start by trying to determine if the stalling is transmission or engine management related and go from there. If the check engine light is illuminated, scanning for trouble codes will likely reveal some insight into what the problem may be. As these sorts of engine management issues can sometimes be difficult to diagnose, I would recommend having a professional technician, such as one from YourMechanic, come to your location to diagnose what may be causing your stalling.