[Speargun]

Thanks for the responses! This is first time that I've run into this problem so I wasn't sure exactly what was going on.

I'll try re-torquing the heads with a different torque wrench. (I'm beginning to think mine is off.)
I'll also check all of the plugs. I pulled a couple to get a reading & they looked good.

To answer some of the questions above:
Heads are 16 large valve.
Cometic gaskets.
No cloud of steam or sweet smell from the exhaust.
Air was purged from system by topping off at a fast idle & burping the upper hose.