Good job. I know how hard BGA soldering can be, you can't easily tell if there's are bridged pads underneath the chip, which could kill both the chip and the console. And those are quite a few pads which makes it all the harder.
I would never have guessed that it would be the RAM. How did you find out?
You probably only needed to replace one of the chips though, but I don't know how much they cost so if they are only a few bucks each it might be worth saving the trouble and just replacing all of them, rather than having to desolder the old one, solder the new one in, if it doesn't fix the problem, desolder the new one, solder the old one back in, and move to the next one etc. 4 times.