on one word... bandwidth.
Google operates huge server centres, but still there can be problems at peak load times - there are just too many people trying to use a free resource at the same time.
Try working when America is asleep - which in general terms means between 3:00 and 11:00 a.m our time. You should find that things go better then.
All that is based on the assumption that there's nothing going wrong at your end, but the fact that you say you have no problem with any other sites makes me think it's bandwidth.