I'm having an issue in the sim at my Addon Manager airports, and I've been trying to mess around with my settings to fix it to no avail.
Your problem doesn't have anything to do with the Addon Manager and, in fact, you will see the same issue with any airport that uses custom textures for runways and markings, which all the good scenery usually have (even those not using the Addon Manager...)
Your problem is not related to LOD either.
Instead, it's caused by not having set Anisotropic filtering on your video card. Depending on the card and the driver, the only sure way to enable Anisotropic filtering (which will prevent blurred textures when seen from a very low angle), is to FORCE IT ("enhance the application setting" ) in the video card Control Panel, and set it to a value of 16x.