The excerpt that best confirms the theme of "the most difficult trials come with great reward" is the first one:
"If in that snowy backyard the driver of the black Buick had cut off our heads, Mikey’s and mine, I would have died happy, for nothing has required so much of me since as being chased all over Pittsburgh in the middle of winter—running terrified, exhausted—by this sainted, skinny, furious redheaded man who wished to have a word with us."
In this passage, the narrator reflects on the intense and terrifying experience of being chased but suggests that the trial was ultimately rewarding, as he feels it was a significant moment in his life worth cherishing, to the point of being "happy" even in the face of danger. This encapsulates the idea that challenging and difficult experiences can lead to valuable and memorable outcomes.