That's pretty unusual behavior.
When you flashed the rom, did you remember format /data and cache first?
I'd make a backup, then try it from scratch to see if it helps.
I only know of 2 people why experienced lag this badly, and I couldn't quite make sense of it. Perhaps those phones had some sort of defect. They were the only ones that froze while doing simple things like generating the debug info in my program. I almost suspect that there is bad blocks in the internal memory, just like hard drives do when it can't read a spot and it tries over and over and over. Maybe PG can add a checkdisk function into his AIO recovery image so we can scan disks for this.
If I had to guess, since they enabled swap file on internal memory by default, maybe it wrote so many times that it prematurely wore out the nand memory, or it was just defective out of the box. This is one good reason to disable the swap file with the optimizer, limit the number of writes because they are finite.
this seems to be what i'm talking about with another phone