I'm in the same camp as you: I love the full name Diana, but what has kept me from it in the past is the possible nickname Di (it sounds like you're telling someone to go die). That said, I've met a few Dianas my age and none of them have used the Di nickname, so perhaps it's fading out of use.
Diana isn't difficult to say on an everyday basis. I also have a three-syllable name that doesn't get shortened (Erica).
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