i only get heat when i accerlate on 2001 Nissan Xterra

i replaced the thermostat the heat censor and put all new antifreeze in the system

Asked by for the 2001 Nissan Xterra
Possible air in system, low coolant level, defective water pump impeller or restricted heater core. Does the temp gauge go up when at idle for an extended time?
3 answers
I agree with wetry ,I would try bleeding the system first
or blend door issues