I fixed it. In APPDATA/Roaming/Lockheed Martin/Prepar3D v4 the DLL.cfg was looking for PACX at <Path>C:\Program Files (86X)\TFDi Design\PACX\PACXBridge\PACXBridge_x64.dll</Path> instead of where PACX is actually installed. <Path>F:\TFDi Design\PACX\PACXBridge\PACXBridge_x64.dll</Path>
Once corrected in now shows up in Addon's drop down menu. If you recall I was having issues with installing PACX in Program Files (86X), not being able to copy and paste Activation Code, so I installed elsewhere, however my installer seems to only like C:\Program Files (86X)\TFDi Design\PACX.