Your overlapping may be insufficient: The tires push down grass during each pass. If you line up your tires with tire marks from the previous pass, the grass does not get a chance to stand back up during either pass. Overlap more than the width of your tires on subsequent passes. This will allow the blades to draw up the trampled grass from each previous pass and should produce a nicer looking cut.
I don't know if this applies to zero-turns: Right hand turns: Twin-blade mower decks are designed with the discharge on the right side. The left blade is positioned slightly forward and in front of the right blade. During left turns this cutting overlap is maintained. This provides cutting overlap when traveling in a straight line. The tractor operator should therefore make mostly left-hand turns when cutting grass.
Improper cutting deck adjustment: This can produce a vacuum imbalance that, under certain circumstances, causes airflow to push outwards from the front of the cutting deck. Consult your tractor Operator's Manual for specific Deck Leveling and Deck Engagement adjustments pertaining to your specific model tractor.
