don't know 1,2,3 but the thermostat sets the temp. if the coolant temp goes up the stat will open and let it cool to the setpoint where it was. or where it used to be.

 

I would tell them that you want the new redesigned radiator. It is noticeable as it is slanted back to avoid hitting the frame.
We have probably put 30 or 40 thousand miles on it with no issues. although it was rubbing in a different spot when we first got it back so I grinded about a quarter inch of the frame back. Now there are no rubbing issues. It was just a terrible design all around by GM.
People have posted here that they have gotten the cheaper aftermarket rads with no problems,so I don't see a problem with it. But I was bound and determined to have mine replaced by GM because this is a design flaw that should have been a recall. As of late though I haven't heard of GM paying at all to replace the radiators that still encounter this problem unfortunately.
I don't know or understand what the deal is with the temp. I wish I would have scanned the temp before the rad replacment. But the gauge inside our hummer definitely went up and constantly is at between 2/3 and 3/4 when it used to read around the 1/2 mark. BUt our operating temperature is normal. So that gauge honestly means nothing unless you see it go all the way up telling you that it is overhating. Only way to truly know the temp is to Take its temperature.