As far as the heater is concerned, I think there is a uncooperative valve that does not work good enough any more.
It seems to me that the valve that has to guide the incoming air-flow towards the heat exchanger is only opened/closed half and that there still is a lot of air coming in the interior without being guided through the heat exchanger...
On the european models (non airco's) this valve was controlled by a cable; I don not know whether the US models are controlled by a cable or by a vacuum pot...
Basically I think you get to much unheated air in your car; the heated air will be warm enough, but the mixture (heated-unheated) is not right and the faster you drive, the more unheated air comes in!
with a minor 600+k