In order to take advantage of the latest improvements Sprint has made to the phone's ability to receive and utilize signal efficiently, updating to the latest ROM is not enough.
There is a special component outside of the ROM itself called the Radio Baseband, which ROM developers don't include (for whatever reason) into the custom ROM images, and instead sometimes provide as a separate update.
For instance, my Hero is using DamageControl 2.08.1, and its Radio Baseband version is 1.04.01.09.21 (the 9/21 seems to be the release date). As you can see, this baseband version is the same as I had in the official Hero 1.5, even though the ROM is 2.1.
The latest Radio Baseband, ripped straight out of the very latest Sprint Hero Android 2.1 update leaked a few days ago - the one that we suspect is Sprint's latest and greatest, is version 2.42.01.04.27 (apparently from 4/27).
Here is what flipz, the developer of Fresh ROM, has to say about using the latest baseband:
Flashing an updated radio will typically give you better battery life and better signal.
Updating To The Latest Radio
The update should theoretically work for all CDMA users, not just Sprint, but I can't guarantee it.
This is also a good time to mention an obligatory "doing this may brick your phone (but most likely won't)" warning.
In order to update to the latest radio image, all you need is to
- download the radio image from flipz's post
- copy it to your phone
- boot into recovery mode
- select the Apply update from .zip file or Flash zip from sdcard option, depending on your recovery image, find the radio image you just copied in the second bullet and apply it
Here is the whole process documented in the screenshots I took. Check out the before and after Baseband version fields.
Now, I'm not sure if my battery life or signal quality will improve but hopefully HTC and Sprint cooked something good.
Source: flipz's blog