I've had the issue for month's too. I used to be able to load 30 minute YouTube movies faster than I could hit the Play button, now it's just dreadful.
I've not been succesful in having them admit it was an issue on their end. I've had Fios for 3-4 years now and this is the first issue I've had, other than the YouTube issue it's been scorching fast, and good picture quality etc. Hoping they resolve it soon!