Southwest Airlines Co (NYSE:LUV) shares hit a new record high Monday but then slipped slightly into the red as investors digested the airline operator’s May traffic results, which showed a 0.6% increase in passenger revenue miles from a year earlier, a 1.5% decrease in available seat miles and a higher load factor. 

Southwest Airlines flew 9.40 billion revenue passenger miles in May 2014, compared with 9.35 billion flown in May 2013. The load factor was 83.7% in May 2014, compared with 81.9% a year earlier. 

The company estimated its passenger revenue per available seat mile increased by 8% to 9% year on year. 

For the first five months of 2014, the company flew 42.7 billion revenue passenger miles, up 2% from a year earlier. Year-to-date available seat miles decreased 1.1% to 52.88 billion from the prior-year period. 

LUV was down 0.1% at $27.57 in recent trading, after it climbed to a new all-time high off $27.70 earlier in the session.