Okay, here's an update... MUCH sooner than expected. I didn't realise LM provided an updates package rather than having to do another full installation. So, updated to P3D 3.4 and ran PF3 no problems. Loaded flight plan, connected, contacted clearance. So it looks like you may have an issue with your P3D install. I see by a previous post you too only updated the P3D client, which is exactly what I did and everything is working just fine.
As a process of elimination try running P3D with no other addons and then retry PF3