My passengerside window keeps returning to half.

You will need to have the BCM codes read. Probably at a shop or dealer. You can try an autoparts store (its FREE), but sometimes they aren't able to read body codes. It's still worth a try.

(This kinda sounds like a faulty limit switch on the passenger side motor)

If you should have codes, please post them here BEFORE buying anything. Hopefully we can hope you diagnose this problem and save a little mony in the meantime.

Here's a reset method for the power windows:
2003 Nissan 350Z window motor recalibration METHOD 1
What you need to do is pull up on the window switch till the window stops. It will probably drop due to being uncalibrated. Pull up on the switch again and let off. The window should stay up this time (you just over rode the pinch protection.) Pull up on the switch again and hold for approx. 3 seconds. Now push the window switch all the way down till it stops then let off the switch. You are going to then push the switch down again and hold it for approx. 3 seconds. Pull up on the switch till the window goes all the way up. Let off then pull up once more and hold it in the up position for approx. 3 seconds. This should fix your problem.

If this doesn't work there is another method which requires you to remove the door panel to access the rest button. I'll type it up and post it also.

2003 Nissan 350Z window motor recalibration METHOD 2

1. Remove door panel
2. With door open, lift up and hold the window switch until the window is fully closed.
A. Do not use the window auto-closing function.
B. Do not release the switch before the window is fully closed.
3. Get inside the vehicle and close the door.
A. You need to close the door so that the door switch (interior light switch) is fully
depressed.
4. Press and HOLD the window regulator motor Reset switch. While holding the reset
Switch, press DOWN and HOLD the window switch until the window is fully opened.
A. Do not use the window auto-up function.
B. Do not release the switch before the window is fully opened.
5. Release the Reset switch. Then, lift up and hold the window switch until the window
is fully closed.
A. Do not use the window auto-closing function.
B. Do not release the switch before the window is fully closed.
6. Open the door to release the door switch. The window glass should partially move
Down.
7. Test the window’s operation a few times.
8. If all is well, reinstall the door panel.
9. If you still have problems, go through the process again.

It's been a while AVG6691, but I am glad that I was able to help.