Manufacturers consider a quart in 600-700 miles to be "normal".
Are you using synthetic oil?
What are your drain intervals?
Are you checking level hot or cold?

There are a number of oil analysis labs available. I normally use CTI (Cleveland Tech ) through AMSOIL. And, there is Analysts Inc, Ana-Labs, QuikChek--search the internet. Your local truck dealer may be able to do this, too.

Depending on the mileage of your car, you should expect to lose a quart between oil changes, sometimes more in you have high mileage or abused engine.

Coolant bypassing the gasket = Milky looking oil, specially under the oil filler cap.

Did you check the oil level at the beginning of the thousand miles?

If someone other than you changed the oil, it is possible that they added a bit too much. I find that the technicians that change my oil often put a bit too much oil in when filling the car.

I have gotten in the habit of checking all the work that I get done as they often make small errors. And sometimes BIG ones.

BTW - how often do you check your oil, I do mine weekly.

If you are losing coolant, a quart should show.

How's your fuel mileage? Fuel in your oil is a much more likely scenerio IMHO.
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3 8s & 2 7s 740,000 miles total