Getting a similar problem. Moved house and my 360 started freezing after a few hours play. Then it started freezing at the start of a game, and eventually 3 red rings with 0102.
The GPU is getting so incredibly hot, the heatsink can barely be touched. This is some issue not related to cooling in my opinion, i have put some artic silver on, but the heatsink is roasting so obviously the heat transfer is working fine, it's either just not dissipating enough (imo unlikely) or for some reason the GPU is creating huge amounts more heat than it used to.
I would like to try slapping a fan on top like in the picture, would be nice to know where to hook the 12v to.
The only anomaly i have noticed is when cleaning the gpu, one of the small chips right next to the main cpu die had the thermal wax stuff down one side of it. I tried to clean it off best i could but it is very difficult, presume the wax is not conductive but maybe it is causing some sort of a short? (stabbing in the dark here).
Thanks