This is something which took a long time for me to discover…
I’m running CyanogenMod 7 (or CM7, version 7.1.1, Android version 2.3.7) on a rooted HTC Thunderbolt (or TB mecha) on the Verizon network. 4G for me was not working, it was stuck in 3G mode.
Normally if you’d like to change the network setting in order to toggle between 3G and 4G, you either use something like the “Phone Info” or “LTE On/Off” apps, or dial *#*#4636#*#* on your phone, and then go to “Phone information” → “Set Preferred network type”
If you do this while running CM7, you will see one of the options as “Unknown” and there will not be any LTE options. Instead, you must use the ROM’s built-in access to this setting via:
Settings → Wireless & networks → Mobile Networks → Network Mode
From here you can set to 4G as “CDMA + LTE / EvDo“, or 3G as “EvDo only” to increase battery life.