Definitely second "Not a Good Day to Die." Michael Lee Lanning's Vietnam journals are also interesting when it comes to care and feeding of troops.
For an interesting fiction twist you might try "The 13th Valley." It's a fictionalized version of 101st ABN combat operations in Vietnam in the early 1970s. Has some interesting observations about the difficulty of leading and motivating troops in an unpopular war. Just about anything by Leonard Scott is worth reading, but especially "The Hill" and "The Expendables."
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