thanks for your reply.
Actually I am already in the USA and on the verge to go back to Brazil. It's been almost 6 months now since I arrived here.
I sent this question because I am pretty disappointed with the level of improvement I reached, which means a certain level o fluency, but still far away from what I expected.
Thus, this made me jump to the conclusion that either my exposure wasn't enough or my expectation was too high. I hope the later one is the case.
That is way I would like to know similar experiences, so that maybe this will comfort me somehow.
Anyways, whatever the case is, I am afraid it is too late now. Further improvements will have to take place in Brazil.
Thanks again for your kind reply.