[KimMG]

When you get your car up to operating temp are both hoses going the heater core hot? Did you flush the heater core? What did the old spark plugs look like? Have you pressure tested the cooling system after you replaced the radiator? What temp thermostat are you using? Did you pressure test the radiator cap? Did you check the oil level? Did you do a compression test on the motor? What are the condition of the hoses you didn't replace? Are they collapsing internally?
Lack of heat can be caused by low coolant level or a clogged heater core.