96 Cavalier heating sorta messed up

I just bought this car, and the heating works fine, but when I start driving on the highway, the air starts cooling off.  Like the faster I go, the less heat it has, until its just throwing cool air at me, but as soon as I get back into town, its hot again.  Whats the deal?

Also, the first three settings are all pretty much the same, throwing out just a little air, like the 2nd and 3rd setting are clogged, or are exactly the same as the first, but the last setting works like it should.

All help appreciated.