If you could post up a log, or better yet, send a log to my email, that would help in diagnosis the problem.
18.5psi on pump gas really isn't that much, granted the griffen fmic isn't the largest, but it should support the boost levels you are attempting to run.
If the ecu is pulling it back to 13 degrees, you must be knocking 10 counts or so? (I forgot what it reads on dsmlink, maybe 3?).
I would double check the gas scenerio, like mentioned.
Following that, I would obviously make sure baseline timing is at 5 degrees, and your not fighting an uphill battle against the ecu. Also, make sure nothing is 'happening at that time' aka harmonic interference (Chris mentioned a VERY good method to rule that out).
Finally, once again, try to post up a little more information to whats happening. Are you seeing a jump in airflow numbers? Injector duty cycle jump?
Keep us posted.
swanny09@yahoo.com if you want to send me a log.
Good luck.
Also, what is the motor setup exactly? (edit* see chris beat me to this).