Idk where the server is located exactly, but I live in Florida get a ping of about 50ish. Where are you located? Maybe the proximity between you and the server has something to do with it.
On a somewhat related note, I too experience ping fluctuations but I've only noticed it happen on AOD Pandemonium. I go from a ping of about 30 all the way up to about 140 at varying times throughout the day.