This is a first install for P3D, but I do have the trainer installed for the GTN 750 in X-Plane. But I did run the "installer" that I was given after purchasing the P3D version to make sure it wasn't anything different and it said I was all up to date.
Also when I first ran P3D it did ask if I wanted to enable the RXP GTN 750 and I said yes so it is an active addon.