This thread doesn't sound right.
I mean sure, I have heard about this particular problem before and it is a real one, but what are the chances that top tier developers mess things up in a way that they forget about making sure DL actually works. They seem to work for 99% of customers so there obviously has to be some other specific, probably even common, issue that is making your simulators behave that way.
As always, wipe configuration files, restore stock shaders, disable all addons and then test. If it works (and it does ... usually), well then you start the elimination process.
