Leatrix Latency Fix is not some magical thing that makes your computer able to communicate with the WoW servers instantaneously without regard for the laws of physics. While it will optimize your computer's ability to communicate with the servers for many online games -- including, but not limited to, WoW -- there's only so much a software tweak can do. The speed and reliability of your connection are still ultimately dependent on the physical hardware (computers, routers, cables, etc.) connecting you to the Internet, the operating systems and drivers running on that hardware, and the sum of all other traffic passing through the same hardware. You're never going to have a perfectly stable connection where every single packet takes exactly the same amount of time to get from point A to point B. That's just not how it works.
Anyway, latency in the neighborhood of 75-135ms is perfectly fine, and I can't really see how a network connection issue would have any real effect on your framerate in WoW. Here's what I'd suggest, in this order:
(1) Do you have the same problem when all addons are disabled? If not, then the problem is most likely an outdated addon spamming the game with errors; the game does not show you addon errors by default. Go into Interface Options > Help and enable "Display Lua Errors". If any errors pop up, disable the addons causing them, or just keep disabling addons until you stop getting errors. Use the
Curse Client to get (and keep) all your addons up to date. Get rid of any addons that aren't being updated anymore.
(2) You mentioned that you recently updated drivers on your computer. Did the problem start right after that? If so, then the issue is probably a buggy driver. Go find older versions of all the drivers you updated, and roll back. Start with your video card driver, as that's the most likely culprit.
(3) When is the last time you scanned your computer for malware?
Microsoft Security Essentials is free and easy to install and use, or there are many other popular anti-malware suites out there. If you don't already have one, go get one. If you do have one, or you just got one, let it do a full system scan.
(4) Look at anything else you recently changed with your computer or network setup, and try undoing it. Did you install some new software recently? Disable or uninstall it. Did you upgrade the firmware on your router? Roll it back. etc.