isx15 cm2350 pushing coolant

[TomHanson]

Kind of an odd duck, wanting some opinions. Engine is demandated with a fresh (aftermarket kit) overhaul, about 15k miles. New aftermarket head as well. Liners were cut to .012in(I already know @rawze 's skin will be crawling for not being set to .014, I apologize lol.) Anyways, this engine recently started pushing coolant. Driver made it back up to us a couple hundred miles away with the cap loose, and did not lose a drop. Engine does not seem to be burning any water, the tail pipe is clean and there has not been any white smoke. The truck can be dead cold, and create 10 psi in the cooling system within 30 seconds of running. I already bypassed the compressor head. Tested for combustion in the coolant system to no avail. With that being said, am I missing something simple here? Don't want to rip the head off to find nothing...