Hi Ryan

Thanks for posting in the Community. Unfortunately there isn't a way to automatically add lines between all shapes simultaneously in Lucidchart. However we are always looking for ways to improve. Would you mind sharing your feedback or any clarifying details about what you'd like to use the letter numbering for? We greatly appreciate your feedback!

Thank you Leah! 

Often times  I will space out shapes prior to connecting with lines. It would be useful to be able to select multiple shapes and have lines added. I can imagine the technical complexity to program this function but maybe if you were to select a starting shape and an ending shape it would make things easier