Here is some information pertaining to firmware updates for Moto DVRs:How to use a Motorola DVR/Firmware and Software
. This also explains how to check your current firmware/software versions.
According to that information the DCX 3400 series newest firmware & software are:
Firmware version: 24.33
Software version: 78.55 - a28p0-5.1008.r-2
Having said all of this, unfortunately, I think you are at the mercy of Suddenlink to update the DVR. Maybe you can try an online support chat with a rep but I'm really not to sure how to request the update.