Add a head shim or go to a cooler plug.
I say check the head shim first. Did you use the shim from the TM button? You're running a TZ turbo button on a OS .18TM so you definately need to use the shim. You may want to add a .01 shim.
The OS .18TM/TZ's should temp at 240 or so. Pushing it more than that is not good.