weird Ls 05 v6 heat problem

[clay]

So it simple when im driving on highway i got heat in my car but when im driving at low speed in city there no heat ?? Winter coming hellllllllp lool

 

[joegr]

Probably air in the cooling system. One of the plastic cooling system parts may be starting to leak. The degas bottle is one of the better suspects.
I don't think that it's a stuck thermostat, but I guess that's possible too.