Intermittently switching from regular driving mode to limp mode

Got this car from a tow yard. What a mistake that has been! It was intermittently switching from regular driving mode to limp mode and the trouble codes indicated and, the shift solenoid pack. On the way to work on it, it started driving in short joking surges at a very slow speeds with my gas pedal all the way to the floor. I replace the shift solenoid pack which one from a junkyard, but from a 2008 PT Cruiser. Can't find where it says where there is compatible but the part looks exactly the same. Now it will start but it stalls out as soon as it's put in reverse or drive. Please help! What could be causing this to happen?