Did you find something that might be causing the problems?
Yes, I managed to connect to one of our testers that has everything from OrbX installed, made several tests, and we were finally able to see the blurries! They couldn't possibly appear with the default scenery but, with the added load caused by the ginormous number of files added by OrbX, allowed to see the problem.
And yes, it was entirely MY fault: when porting the Addon Manager code from FSX to P3D4, the most difficult part wasn't porting to 64 bit, that was easy, but rewriting lots of code to support Unicode. A single function wasn't converted correctly, and that slowed down the file access, but it could be noticed only if the simulator was already overloaded by other addons.
And no, Couatl and GSX didn't had anything to do with it...it was just a single line of code in the Addon Manager which I overlooked.
Excellent news! I have P3D 4.3, and do indeed have Orbx Global textures, NA Landclass and Vector. The global textures probably don’t add any additional load, but I’m sure that Landclass and Vector do.
I just re-flew the flight to KDTW that was causing major performance problems, and it worked perfectly with the new Addon Manager. Thank you for your diligent efforts to get to the bottom of this problem.