[rootlinux]

Probably a bad flash?
What radio did you flash? Make sure the radio matches your device.

Here is what I would do.
Flash back to a stock rom.
Flash your radio and test to make sure everything runs up to speed without errors.
If it is good then flash to custom rom.
No need to re-flash radio because custom roms do not usually contain a radio. ( non that I have seen )

Test it again and see if that fixes your problem.
Test before installing any apps or anything.
If it runs fine then slows after you install anything you will narrow down what is causing it.