It's not rocket science. Do a little search on "sms lag fix" and see the first topic that comes up. It explains how to do the fix manually as well, so you can see exactly what it does. It doesn't "break" anything. And as soon as you apply the fix, and soft reset, there is no more lag. Simple as that. Who cares if you just flashed or not, just apply the fix if you're having the problem and be done with it.
This is the post by the way:
http://forum.ppcgeeks.com/showthread.php?t=73005