I had a similar problem with a 350 Chevy a few years ago. Started right up when cold, no matter how cold, but wouldn't hit a lick when warm. It would spin over, but wouldn't fire. I would run the battery down trying to start it... Turned out to be a sloppy timing chain! I know you said this is a fresh engine, but maybe something has a defect or cam timing is off. Just a suggestion of something to look for...