Hi there,
First of all, congrats on an outstanding GMAT score! A 750 is rare, and no you do not need to repeat it!
The AWA of 4 is not ideal but it's just below average generally, it's not a '2' or '3', and the primary focus is on your overall GMAT score which is meant to predict your success in b-school, and it seems you've shown you can definitely handle the academic rigor of the program!
Please know that b-school admissions are not based solely on test scores, stats, or formulas though... the schools really look at your whole application holistically and decide whether you are right for the school, and whether the school is right for you. They look at your academic ability, yes, as well as your professional experience and your personal traits and character. They look for evidence of leadership and teamwork and initiative and creativity. They want to know what makes you unique and what you'll bring to the class. They want to know what your career plan is and why you NEED the MBA to get there, and to see that your overall story makes sense (your past + the MBA = your future goals). They want to know why THEIR school is right for you! So there are a lot of those key factors that need to successfully be demonstrated in your applications-- namely in the ESSAYS!
It's tough to say without seeing your full application, resume, and essays, but likely there were some missed opportunities with demonstrating some of the pieces above in the prior Duke app. (Side note-- we do offer a 'Ding review' if ever interested,
https://www.mbamission.com/services.php?package=ding).
You do have a challenging list of schools here, and there are a lot of well-qualified engineering applicants applying, so it can be difficult to stand out. You may want to consider some schools in the 15-30 rankings for a safety option or two, just a thought.
Beyond that you can sign up for our free 30 minute consult if you'd like to chat through your profile in more depth, or come back here with additional q's. Wishing you the best!