Since you have Detroit cams, I'd pull the cover and inspect the cam and rockers. You have have scoring on the cam and/or a broken rocker. Or, your tensioner could have failed and not be keeping enough tension, or your chain jumped.
Since you've ensured it is not a plug or cop issue, and since the cams were replaced, the logical choice would be a mechanical issue there, assuming the alternator is producing 14 volts and you have adequate oil pressure.
Mike - 2005 Stroked/Forged/Cammed V8 (5.0L.); Kenne Bell 2.6 @ 18psi, + many mods. (formerly a V6 w/Vortech supercharger);
- 2006 4.0 V6 with PH Turbo and TR6060