My 2005 Tahoe had something similar BUT my recirc door never worked and I never fixed it I could get by without it. Here recently I had symptoms like you mention when it gets really hot outside. Has freon, pressures all good, rear blew colder than front. Changed out the recirc door actuator (I didn't think this would fix it).
So now when I drive around and start to wonder why my a/c isn't blowing cold I realize I didnt push the recirc button, now it is so cold I have to turn it down when it is 90+ outside.
So short story is - does your recirc door work, as in you can hear the difference in the air flow when you turn it on?