Welcome to OPM! In my experience, AdComs LOVE to see military people apply to their programs. Your USMC background will be a large feather in your application cap.
Regarding changing majors: man is this a can ‘O’ worms. In a nutshell, do not select your major based upon what you think the AdComs desire or will smile most favorably upon. Do select your major on what ‘melts your butter’. Because if you love what you are studying, no matter how difficult it is, you are far more likely to do well in it. No major is given special consideration or brownie points.
Now, no doubt about it, engineering is among the toughest majors to do well in - but you seem to have exceled with a 3.8! I would say that if you feel that it is more trouble than it is worth & you feel as though you are wasting time & effort to do this well in those course, it would/could place you at higher raisk for academic fatigue…or a case of the "I don’t give a shit"s. If it occured, it could damage that pretty GPA. So, were it to be me AND I had another major in mind that really tickled my fancy, I would change. BUT, if engineering is your thing & you love studying it, by all means, stay with it.
If you do change & end up with course slots to fill. Instead of trying to sprint to the finish, you might consider investing some time & effort taking a few classes that are of interest & on topics you would not have considered previously - i.e. when you are on a hyper-focused trejectory. For example, I took Fantasy Literature & Art Appreciation for the hell of it. 1 - It is good for the squash to study things non-science & 2 - The AdComs love to see the ‘well rounded’ applicant package.
I would stick with industrial engineering. Like you and Dave have pointed out, you have done very well in the major and you are going to stick out. You have a military background and you are applying w/ atypical degree. If you enjoy Industrial Engineering you are more likely to do better well academically then switching to the biological sciences because everyone else is doing it. Then again, if you really like biology and want to switch it - I say do it. You only go through college once (for most of us) so make the most of it and have a good time.