If your gear is good and your ISP is good (their server host) it could be an issue with a node or nodes between your local network and GT's server. That's the good news. The bad news is that your ISP will probably not be able to do anything about it nor will GT...the problem will eventually 'go away.' As mine did.

I got lots of help and advice from the GT Help Desk when my problem surfaced off and on for a couple weeks in April. The problem node was probably identified but neither my ISP nor GT has much say or pull with the backbone providers who operate those nodes. It just corrected eventually.

Or...at least that's the way I understood the problem then. Don't feel alone although, for this problem now, you probably are. :D