Does P2A recognize the transponder in third party aircraft like the PMDG NGX or the FSL A320? I don't have a problem in X-Plane but in P3D I never get a radar contact call so I'm constantly being told to squawk XXXX.

There are some 3rd party aircraft that don't implement the avionics in a way that FSUIPC gets the changes to settings.

  On the transponder, just be sure that the Transponder Mode and Code in the upper right of P2A are correct. 

To change either of them in P2A, just click on the value and it will either cycle through the possible values (Mode) or pop up a Transponder box where you can set the code and the mode (Code).

Dave

Thanks for the explanation.