I've noticed the last two years my 2008 GP Base takes a long time to blow heat.
If I set my HVAC to max heat and max blower start the car while the engine is cold, it takes about 15 minutes before the engine temp gauge starts to make it to the first tick mark, then it starts to go up to the 2nd tick mark and stays there.
When it gets past the 1st tick mark I get warm air, and the 2nd it is hot, but when I first got this it took probably 5 minutes at most to get hot air.
I replaced the thermostat in it, topped off the coolant thought it got a bit better but now it's back to taking 15+ minutes to warm up.
Over summer I did notice when I do heavy acceleration on the highway you'd hear water rushing in the heater core, which I never heard before.
I tried to burp it but seems like nothing helped, not sure if air is trapped in the core? I get heat but it takes forever.
Also haven't had the coolant flushed yet, it's at 60k miles probably time for that also?