Finally found this: https://mitsubishitechinfo.com/epacarb/PCMUpdates.pdf
TSB 13-13-001rev11 seems to be an official updage to solve "MIL Illumination, DTC P0300" problem. This is the version they reprogrammed my car.
So far it looks that the dealer correctly followed the Mitsubishi procedure for the problem.
But still, I would be curious to know if other had the same problem.
Also, my 2012 GT does not sound as smooth and as good as my older 2009 GTS. When I start it, I always have the feeling it will stall, but it don't. It is like this since new. It might be normal, but I wonder if others have the same feeling with their GT.
Thanks in advance for replies.