However, upon installation the SODE manager doesnt register due to "dll xml cannot be found" error and upon loading the aircraft the message pops up saying couatl has encountered an unrecoverable problem.
This error clearly confirm the problem doesn't have anything to do with GSX, since even SODE cannot find your DLL.XML file.
The usual reason for this problem is having used those "migration tools", which are very dangerous and known to screw up your installation entirely, just to fool installers made for FSX to install into P3D. Which if of course very risky, because it will mess up entirely with PROPER P3D products, that support both properly, and must recognize them as they are.
It's likely your registry is corrupted, possibly pointing to the wrong folders, maybe the FSX ones, if you use the migration tools.
In addition to that, if you really insist using P3D3, at least try to use the latest version ( 3.4 ), since from that version on, we no longer use the DLL.XML method, but the add-on.xml method, which is more reliable.
I suggest reinstalling the sim, and use the latest version.
Of course, the real solution would be switching to P3D4, which is a far better product. Note that, it's very likely we'll stop supporting any version of P3D below 4.4 for the next updates. It's becoming almost impossible for us to support so many simulators, and many other developers are doing the same.