on my 60 to get the heater to work like it is supposed to I had to machine a restrictor to slow the water down goin thru the heater core. I only drive my truck when it is real nice with no chance of snow in the winter months and not much at all in the summer but the few times i did when the weather was cold it was torture before I fixed the thing. Do you by chance have the deluxe heater? When I first put mine together I had a problem with the blend door sticking open also letting air from outside blowing by amplifying the cold air coming in.
