After the Carrier IQ debacle on the HTC EVO 3D (among other phones), CIQ was removed from subsequent builds of the stock ROM and the radio firmware was updated to 2.17.651.5. The removal of CIQ also appeared to extend the battery life and improve the speed of the phone all around, possibly due to it not hooking every action and logging every event, or perhaps due to better coding in general.
Root users had previously reported a significant battery gain just by stripping the CIQ process from their phones, but the thing was so ingrained in the system that even rooted ROMs often had to have kernels with dummy CIQ responders.
As development has gone on since those days, more ROMs are being developed for the new base, and although they somewhat work with the older radio firmware, they're prone to lockups, variable performance, and general fits of weird.
S-OFF users (people who got in with Revolutionary before HBOOT 1.50) have few issue with updating the radios; they can just download and flash a radio update from recovery because they're S-OFF (and cooler than us 1.50 unlocked/S-ON kids by default). But if your rooted EVO 3D isn't lucky enough to be S-OFF, then it's not quite that simple.
The process is actually pretty straightforward, but it's very time consuming. Set aside an hour or so depending on how much data you have, and at the end you should have the new radios installed, which is great if they work with your ROM, but terrible if they don't.
So, understanding that if you're S-ON you can only flash firmware/radios forward, not like those cool S-OFF kids (get off my lawn!), and are willing to take the risk that you'll be potentially stuck with a ROM that you don't like and perhaps a kernel selection that's different, read on.
Oh yeah, and to cover my behind, I'm not promising I didn't miss a step, so you know, proceed at your own risk.
Step 1: Nandroid backup
If your recovery allows this, back up .android_secure and /data also
Step 2: Titanium backup
You can probably skip this, but better safe than without data. Alternately you can use many other fine backup programs.
Step 3: Backup to a computer
Mount the SD card to your computer, make a folder called "backups of my phone," and copy the contents of the SD card here.
Step 4: Lock and RUU
This step will wipe your phone and return it to stock locked unrooted and with stock recovery. The only difference between your phone after this and a new phone out of the box is it will say "re-locked" in HBOOT as opposed to "locked" or "unlocked."
Step 5: Update firmware and radios
On the off chance you have an older RUU or that your carrier (Sprint for most of us) released new radios, go in and update firmware, prl, and profile from Menu > Settings > System updates.
Step 6: HTCDev unlock
This will also wipe your phone. So keep that in mind if you did anything between step 4 and now.
Step 7: Install a custom recovery
You'll need to have recovery working again in order to restore your Nandroids or flash root tools. This is covered in the link at step 6.
Step 8: Restore backed up data to your SD card
Mount the SD card to your computer and copy the contents of your "backups of my phone" folder (created in step 3) to the SD card.
Step 9: Recover the ROM
Reboot into recovery. Install a new ROM or Nandroid your old ROM back, keeping in mind that your old ROM may not play nice with the new firmware.
Step 10: Finish the fight
Assuming you installed a new ROM as opposed to recovering an old, use Titanium Backup to restore your apps and data one at a time.
You should now have a phone with the new radios, and it should be able to play nice with things built for the new base.