Another suggestion (which you may have already tried, so forgive me if this is old info) is to make sure you have the correct Radio and bootloader for the build.
Most current custom ROMs require olipro's 2.4 bootloader
http://forum.ppcgeeks.com/showthread.php?t=9093 and if you don't have that installed it will produce exactly the effects you're talking about. An incorrect/incompatible radio could produce the same effect.
Also some roms (notably no2chem's) have that problem if you don't do a hard reset and remove the battery for 2 min or so immediately after flashing the rom.
Just some things to try. Good luck.
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- Taxilian
Disclaimer: 87.4% of all statistics are made up on the spot. Author is not responsible for any inaccuracy in his posts -- If you were foolish enough to think that he actually knows what he's talking about and bad things happened as a result, he takes no responsibility for that either. Not responsible for shin damage due to software not working on your girlfriend's phone. Author is also easily amused.