I don't think it's overheating, my drive home and to work was normal, just the water temp all the way and coolant temp at "---"

Should only lose about a pint. Make sure the Pressure System is full, not just the tank. Never mind the last sentence, if this is a 2006.

Wait a minute. donbrew, are you saying that both overheating and too slow of a warm-up yield: the ' ... ' digital temperature reading, temperature gauge pegged cold, and no AC? Are you kidding me! Have the GM engineers lost their %%&&& minds!

Will it harm the coolant system if I don't replace the radiator fluid? The dealership had already flushed and replaced all fluids before I bought it

Of course not - it is totally reusable. You can drain it low enough to pop off the thermostat housing - drain via the drain petclock on the bottom backside of the rad. Just collect it in a small bucket. Then when the thermostat is replaced, pour it back in.

If you got a CEL lighting up - you need to get the error code via a code reader - hit up an auto parts store who should read the code for you for free.

Lastly - when someone asks you if your A/C is disabled - please don't reply "no, it's blowing warm air"- you need to reply "yes, it's blowing warm air" - it confuses those that don't read internet. :-)

No, and no.

Haha I completely understand, I'm a new and learning "car guy" so a lot of times simple car concepts are foreign to me. Also a musician for what it's worth ;-)
Anyway, my buddy Matt came over tonight and we replaced the thermostat, and topped off the radiator fluid. Ran the ac hot until it was hot to touch, and all was well.

Just for kicks too, I disconnected the rear battery to rid myself of the CEL, and now I can also remote start the vehicle as well.

Very happy man I am now!

Now the next thing to do is get the new power steering assist motor and we'll be good to go!

Good deal man!!! When I replaced my thermostat, I set the Digital display to the temperature display and watched the temp rise as the engine warms up - it's semi-interesting from a nerd point of view. LOL

Well, when the car goes into "limp home" mode the temp does indeed go to ---. At least my 2008 did after the temp got over 241 F, more than once just before shut down. I don't fault engineers for that, as you should not really care what the exact temp is if there is copious amounts of steam under the hood. It is called "overload".