In the owners guide it does state under:
Uconnect 8.4/8.4 NAV Phone
TIP: Your mobile phone must have the full implementation of the Message Access Profile (MAP) to take advantage of this feature. For details about MAP, visit UconnectPhone.com.
Apple iPhone iOS 6 or later supports reading incoming text messages only. To enable this feature on your Apple iPhone, follow these 4 simple steps:
iPhone Notification Settings
1 — Select “Settings”
2 — Select “Bluetooth”
3 — Select the (i) for the paired vehicle
4 — Turn on “Show Notifications”
TIP: Voice Text Reply is not compatible with iPhone, but if your vehicle is equipped with Siri Eyes Free, you can use your voice to send a text message.
Perhaps a call to UConnect support is needed...