PS3 resolution changed after an update

hello
I have a fat ps3 80gb, and i have a problem, when i play call of duty modern warfare 2 or 3, not all the time, but sometimes it runs for about 6 to 8 minutes on gaming, and the system shuts off, with only 3 beeps and a red blinking light, no yellow light.
Now I remember when playing these games, my PS3 runs them at 720p resolution, but now all of a sudden its running them on 1080p. Did the 4.60 firmware update changed this on PS3 to run games at full 1080p.
Maybe thats why my system is turning off due to high resolution.
Thanks