Unfortunately, I don't think anyone really knows what the actual changelog is for these radios... the list of changes isn't really released from the carriers... it just comes on devices and/or updated ROMs from devices and peeps rip them out to share with the rest of the devices.
General rule of thumb though, higher version = less buggy / better radio. It's typically recommended to upgrade to the latest version release whenever you can, afterall it only takes a few minutes.
Here's link for 3.42.30:
http://www.lifesnotsogood.com/dcd1182/titan/radios/Titan%20Radio%20ROM%203.42.30.rar