Well, that's the problem with the reflow method, it's using the same shitty solder as before. This is the real problem, not usually the CPU or GPU. The chips get to a temperature where the solder begins to melt, at which point they begin to lift from the board. So reflow is only a temporary fix. So far mine has gone a few weeks with no problems. I've been trying to keep it flat so even if it gets too hot the chips won't shift as much.
Like I said before, the only way to permently fix it is to get a reball kit with lead solder balls. I think I saw some on Ebay for around $60. Of course, if you feel you don't have th know-how or experience to do that type of fix, I would suggest either sending it back (which i think costs ~ $150) or just invest in a Slim.
