For those who are still having problems loading add-ons after latest patch. Try this one. I have very picky add-ons, this worked perfectly.

change log.

v2
1.0.1103.2
updated gameconfig.xml for lastest patch (mp gunrunning)

some add on cars seem to be crashing when spawned. Im looking into this. not sure if its a gameconfig issue or an issue with those particular add on cars.