Q: Transmission problems.

Hello. From what you describe it would appear that your vehicle may be experiencing more than one issue. If the engine is stalling and jerking when you put it into gear then it may be possible that there is an issue with the engine management system or transmission. If the engine was recently replaced then it may be possible that the issue is related to the work that was done. A few things I would check are the transmission fluid and the idle air control valve. Automatic transmissions operate using fluid pressure and can have issues if the transmission fluid is low or dirty. I would also look at the idle air control valve, which is located on the vehicle’s intake manifold. The idle air control valve is the component that adjusts and maintains the vehicle’s idle speed. If it has an issue the vehicle may experience all sorts of problems, including stalling. If these check out then it may be possible that there is an issue with the vehicle’s fuel or engine management systems. I would recommend having a professional technician, such as one from YourMechanic, come to your location to diagnose the cause of your stalling and hard shifting.