I have been tasked with getting the PD at least two, possibly three, HMMWVs through the LESO program for our department. I am trying to figure out the things I need to look for. I am fairly certain I want a 6.5 Turbo truck, with overdrive. Obviously, I want the newest ones I can find, but what years are cutoffs, and which ones do I look for? Anything else I should know?

check out Steelsoldiers they might be able to help you more.

Flashoffroad.com tech pages will give you a crash course on problems to look for. It's primarily geared toward h1s but has lots of info about the basic info about the mechanics (pretty much identical) without going full blown tech manual. You're not likely to get service record on a HMMWV so checking things like slop in the drivetrain and steering on a lift can be pretty helpful. They require tons of maintenance already so even if you miss something it won't be the end of the world. On electronic 6.5Ts, relocate the PMD as soon as possible. Good luck.