The track would be nice just to get the feel of solid terrain under you feet, but the treadmill is nice every once in a while. You should be fine doing both. Just keep it up you’ll get it!
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put the treadmill at an incline of at least 2 to offset the differance of running on a track. You will feel the differance and it will be more like running on the track.
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Yes, running on a treadmill will help.

But you have to run outside as well.

A treadmill does not duplicate the shock on the knees, thats why you can run further and faster on a treadmill.

You might want to increase you outside running distance.

You will need to run further than your PT test.

3 miles is a good distance.
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There are two factors which contribute to you PRT score. Endurance and speed. Long runs on the treadmill will improve endurance. Short fast runs will improve speed. You should do both. Take a look at the runner’s world web site for some ideas http://www.runnersworld.com/subtopic/0,7123,s6-238-244-259-0,00.html the short runs are easier on the track for most people. You should also run the PRT in as close to the test conditions as possible to gauge your progress.
Good Luck
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