96chevy cavalier ohv 2.2L that cools right down to 40 degrees c at highway speeds plus no heat lower city speeds you have heat and it run normal operating temp thermostat changed and not stuck open?

If you are saying that at highway speeds it is running at 40 degrees celcius (and it isn't extremely cold out), I would say that your thermostat is sticking open. I know you put a new one in, but every now and again a new thermostat will either stick open or shut. If you do the work yourself, what you can do to test the thermostat is to remove it and put it in a pot of boiling water, you should see it open up. Now remove it from the water and watch it, it should close up in a short amount of time, if it doesn't you need a new thermostat. If it is working, I suggest making sure that the cooling system is completely full with no air in the system. If this doesn't work, you might want an expert to take a look at it. Hayden