TIR does work in P3D, all versions of it. To get it to work you have to do this.

P3D DOES come with the FSX Simconnect libraries, for the precise reason to allow backward compatibility with FSX Simconnect clients, and they are supposed to be installed automatically.
They are located in these folders
\Lockheed Martin\Prepar3D v3\redist\Interface\FSX-SP1\retail\lib
\Lockheed Martin\Prepar3D v3\redist\Interface\FSX-SP2-XPACK\retail\lib
If for some reason they haven't been installed automatically by the P3D installer, you might try launching the .MSI files in those folders.

After installing both files, meaning locate and click on the simconnects install files which are already there... no need to install anything else you just need to execute these two files. (in the locations listed above) TrackIR worked instantly!

I used this and it worked so I thought I would post this in our forum so others don't have to do endless hours of search like I did