07 Murano heater only works while driving

[Z31 fan]

I have a 2007 Nissan Murano, the heater only works when driving then goes to cold at idle, most say it's due to air in the system, but I have burped it twice now uphill. I filled the reservoir up pretty good and nothing moves in there, heater core is also fine no weird smells or leaking, I did however replace the alternator and to do that the radiator has to come out. So I took the radiator and radiator fans out and the duct work out to remove and install the new alternator, if there is anything during that process that could cause the issue I'm having with the heater only working while I am driving I am all ears. Please help me out it's fairly cold and the heater is only working while driving and heater core is fine