2006 Chevy Tahoe heater problem

[andrew9163]

Wife's 2006 Tahoe will not heat up. I drove it yesterday and the temp. gauge was showing hotter than normal. Normally runs a little less than 210. It was running about 240. Heater would blow cold air. When I would stop at a light, the temp. would drop down to normal temp. and heater would start blowing warm air. Any ideas?

[andrew9163]

Forgot to add, when I would get back up to speed, the temp. would again go up to about 240 and heater would again start blowing cold air.

[gmtech4]

start with a core backflush and have the rad flushed to ,it seems when engine is not working it cools down and the slow hot coolant is able to give off some heat ,IDK WTF i mean..!!!!!

 

makes no sence