98 Cavalier Thermostat Problem?

[birthofamule]

OK, here's what's happening. About a month ago, my 98 2.2 ltr Cavalier started overheating. So I flushed the system and changed the thermostat. Then the water pump blew 3 weeks ago, changed that. Now I have no leaks, good pressure, have heat. But... I drive on a major interstate to work every day. When I get onto the highway, after a mile or so, the temp gauge drops down about as far as it can go. Car barely blows hot air (I'm assuming because fluid is so cool) When I am not on the highway, the temp runs at about 3/4 to red, not overheating, but pretty warm seeing it's been about 20 degrees or below for about 3 weeks now.
My question is, do I have a bad thermostat? I bought a 195 degree Duralast thermostat. This is what the autoparts guy said I needed, which is in line with everything i've looked up on it. Somebody please help!

Thanks,
Birthofamule