not a mopar question, 09 chev uplander

Has anyone owned or work on the 09 Uplander 3.0, my problem and what i have read they all have it.at idle it blows cold air when cruising below 1600 rpms its cold once i get past 1700 rpm hot no problems with the cooling system it reaches full temp, the coolant level is spot on.can anyone help.the rad shop says its a block in the heater core, but when i go on line some have tried that ,it help for a week or so but came back, there should be a recall but nothing.