None of the dev ROMs include a radio.
Largely because radio firmware comes out so infrequently, there is no reason to take the risk of flashing to replace the radio firmware with... wait for it ... the same version of radio firmware.
Check your Settings -> About phone -> Baseband Version. The latest is 2.42.01.04.27; it was shipped with the July 2010 OTA. If you have that, it's as good as it's going to get.
If you have an older radio, you can install this "update" package. It is a "no-wipe" install, as you might expect:
Make sure your phone is "well charged" before you flash it - 100% charge is a good number to start with.
I hate to burst your bubble, but it is quite rare for incremental updates to stable radio firmware to have any effect at all on reception, despite all the nonsense you see spewed on forums like this to the contrary.
And as for "Bars", there is absolutely no standard for what "1 Bar", "2 Bars", "3 Bars", or "4 Bars" is - a ROM provider can interpret the real-time signal data any way they damn well please to come up with a "Bars" to display on your phone. That's why you can switch from ROM to ROM and observe "more bars" - but your signal is no different (especially if the radio firmware didn't change, right?)