Truck wont start one day but it will the next?

Hi I have a silverado with a 5.7 vortec motor. Every so often the truck wont start. It turns over till it floods and wont start till it sets. My father is a mechanic but doesnt have the time to look at it because after 24 hrs or so it will start. It has plenty of oil pressure around 60, it is getting plenty of spark, and it is getting fuel cause we can smell the gas after it floods, also I would like to note it is good gas. It has its moments about once every month the past 4 months. Thank you