i have been working on my cavalier for 2 months now, and i still have no heat unless i'm going slow, as soon as i speed up, the temp goes cold. I bought a new thermostat from autozone and a new cover housing from the chevy dealer. the housing doesn't fit the thermostat, because there is a wire in the housing. do you need a special thermostat from the dealer, or what?!?!? someone please help!!