I do have heightened/more sensitive senses. Is my hearing more acute because of the sensitivity? If you mean I can hear higher and lower pitches than most people can, and hear quieter sounds from farther away, then yes. However, I also have auditory -processing- issues, and while my hearing is great for noticing sounds most people can't even hear, many sounds (especially human voices) can sound muddled or ambiguous to me, so I'm not ideal for eavesdropping on conversations.
At the original poster's situation...
The thing is, if you hear someone talking badly about you form farther than they think you can hear, confront them about it. But don't do it in a way that will make you seem like you are initiate something. Just take something they said about you, quote in front of them, and then question them about it. For example, if you hear "*your name* is so stupid" etc etc, just call out to them or walk up and say, "Hey, you think WHO is stupid?" or "Woah, are you talking about me?"
Or just say "I can still hear you" or "The feeling is mutual" if you're -entirely- sure they're talking badly about -you- or a friend. (I dont know if you ever have hearing mixups, but be sure you catch the name of the person they are talking about. They might even be talking about a different person with your name. That's something I've encountered in the past.)