Yes full race build, bathed, tested, honed, bored, machined, balanced, overhauled. But pretty sure LS3 are made in 'Merica, not too much bad to say about the production facilities and protocols. Poor oil / air separation (PCV) I think. Exactly. But one thing for sure this 2015 6.2 (340) tune is the only difference to previous, never had such an issue like this before now. True. Perhaps the solution in light of tune restrictions is to swap in high quality forged asymmetrical pistons: Piston Slap and Asymmetrical Pistons Cheaper than supercharging, huge efficiency gains, no noise.