Do you have Perforated Tiles or Floor Grates? Are they located in front of where the hottest racks are?

If necessary, rearrange or change to different floor grates so you match the airflow to the heat load. Be careful not to locate floor grates too close to the CRACs. This will "short circuit" the cool airflow immediately back into the CRACs and rob the rest of the room or row of sufficient cool air.