My Connection is TERRIBLY UNSTABLE! Please someone Help me!

Hi all...
I can't figure out what's going on with my connection!
I have a good ISP speed (10mb download 800kbps upload) and i don't have lag problems playing any other game (retail aion, swtor, tribes, etc)
But with Gamez Aion some few times it plays with 200ms (i'm in brazil, constant 150ms would be fine for me) but the weird thing is that the lag is extremely variable...
sometimes its 600ms, sometimes the game stops for about 5 seconds or more! there is something really messing up with my connection...i NEVER could do a pvp without lagging and seeing the end of it with me dead.

I have friends here from Sao Paulo who play fine with about 60ms and they have the same ISP as me
I'm already playing with antivirus disabled.

any suggestion???

thank you