Just got hold of a 2001 Chevy Blazer, V6, Auto, power locks/windows, remote keyless. Great shape, except for the heat.
Symptoms:
Vehicle holds steady at about 185 degrees.
Heater core hoses not hot at idle, but will get hot quickly at 2,000 RPM.
Air temp is about 75 at idle, almost 120 at 1,800 rpm (highway 55 mph)
Reverse flushed and straight flushed heater core, and it's showing very good flow.
Truck reaches operating temperature at about 8 minutes at idle.
Anti-freeze and water are topped off.
Hoses are in good condition. No leaks to be found. She is tight!

Question:
Could this be the water pump? The water pump on my Dodge Dakota failed, but it spewed water everywhere. Is it possible for the impeller to "wear out". The blazer is my oldest vehicle, but it is quickly becoming my favorite because of the way it drives. It is definitely worth investing in. I would like to give this vehicle to my daughter (17!! New driver!), as it seems the safest and sturdiest.

 

Vehicle holds steady at about 185 degrees.
A "good" thermostat begins to open at 195F, and regulates just under 200F. Yours is about 10 degrees cool. Probably needs a new thermostat.


"Heater core hoses not hot at idle, but will get hot quickly at 2,000 RPM."
Classis sign of being low on coolant. Probably has an air pocket and needs to be "burped", and a new radiator cap, (very common problem).


"Air temp is about 75 at idle, almost 120 at 1,800 rpm (highway 55 mph)"
Confirms that it needs a thermostat, and that it has an air pocket. Register outlet temp should be ~130F. Both heater hoses should be very close to the same temperature, and too hot to hold with a bare hand.

 

By burping, I suppose there is a way to do that? lol The only way I can think of is run it with the radiator cap off and fill it under RPM of about 2000? I will definitely get the thermostat and radiator cap, though! Thanks for the info! My daughter is driving it now, and she loves it. It's a great ride, just need to get this heater problem licked.

 

My 1997 Bravada has the same lack of heat issues and I've done everything that has been suggested. In fact, I'm on my 3rd thermostat - 195 degree Super Stant. Each one that I've tried has been manufactured by a different vendor and none of them have yielded more heat. I've just learned to live with it.