I'm not familiar with the maxima fan, but I had very similar problems with a Chevy pickup a few years ago.
After much head beating, it came down to having a properly designed shroud that would pull air across the entire radiator, not just a portion of it. When I took care of this, the situation with my chevy was greatly improved.
In addition to the shroud, I had to fabricate a panel to completely separate the air in front of the radiator, and the air behind it.
Sounds kind of like a "well, duh..." solution....but seriously, the 1.5" gap along the top of the radiator was a problem. At low speeds, it allowed hot air from the engine compartment to be pulled over the top of the radiator, and back through radiator. This was not an issue when moving at higher speeds because of the high[er] air pressure area in front of the radiator. As soon as I blocked this off, my problem went away completely. This gap was originally covered by the OEM fan shroud, which was tossed when I went with an electric fan (after a motor mount failed, allowing the engine to roll over enough that the fan met the shroud, shattering it, and sticking a big chunk of it into the middle of the radiator).
"Life is meant to be enjoyed, not endured" ~someone