Heater going out?

[TODD 2000 V6 CAMARO]

Hey guys, long time, no post. Anyway, I am having trouble with my heater in the old V6 Camaro. I used to be able to get convection-oven-like hot air from the heater as soon as the engine began to get up to temp. Recently, with the area experiencing colder temps, I noticed that it takes about 20 minutes to get even warm air from the vents.
The car did overheat a week or two ago. The car was parked in a parking lot while I ate my fast food dinner. Upon backing out of the parking spot, I noticed the "check guages" light was on, then saw that the temp guage was pinned on the hot side. So I immediately shut it off and raised the hood and let it cool for a while. I checked the coolant which was fine, so started it back up and it ran rough as all get out. So I shut it off again and waited a few minutes, getting really worried that I had cooked the engine. Then restarted it again and it went to a smooth idle. I got out and listened under the hood while it gained temp. I heard the thermostat opened and checked the guage and sure enough it was staying at the normal operating temp. I went ahead and replaced the thermostat anyway. The old one, I noticed after taking it out, was really hard to open with my fingers, while the new one was fairly easy. I don't know if this has anything to do with the heater, but I have noticed that while the car doesn't overheat at all now, it will at times run way cooler than usual. Maybe that has something to do with it?
All I know is even though Texas doesn't get real cold, 34 degrees feels pretty dang cold in the morning on the way to work. If anyone has any idea what the problem may be, I would greatly appreciate the feedback. I am just hoping it isn't the heater core going out....

[Joe 1320]

Start with a complete flush of the cooling system. The heater core is literally a small radiator located in a compartment on the firewall. When you activate the heater via the HVAC controls on your dash, a small valve allows warm engine coolant to circulate though the heater core. If you aren't getting any interior heat, either the heater core is plugged or filled with sludge and not allowing circulation of coolant, the valve is not working so that it doesn't allow the coolant to circulate or the HVAC controls and it's vacuum lines are not funtioning.

[Injuneer]

What temperature is the replacement thermostat?

[Wild Willy]

Yes- what temp does the new thermostat open at? Most factory ones are around 180 or 190 degrees- staying closed until the engine heats up, to quicken the warm-up and minimize pollution from the richer cold-start cycles.

You might want to back-flush your heater core, pull the hoses off the engine side, leaving them attached to the core itself, and running plenty of clean water through it from both directions until the water comes out clean. Also, make sure you don't have an air pocket trapped in the cooling system, hard to burp all the air out after working on it- like, say, replacing the thermostat.