so your not far from me, I would have to go through the same issues. I would get the original mechanic on the phone and tell him your not happy as he recommended a part, you changed it and it is the same. I am not sure what you mean advised and checked by the mechanic, but you have had two mechanic tell you its the same thing replaced it twice and it didn't work. so either you did something wrong and wrecked two parts (not my first guess) , or there is something else to the installation procedure that you don't know. like maybe calibration the new throttle peddle, but you say its plug and play. did you clear the codes when you did the installation?
it could be the main computer its self or the wiring between them, we would only be guessing. I would suggest getting the factory to recommend some one in Alberta for you who might be able to help you troubleshoot the issue better.