LS Backfiring issue

[IndyNova]

Hi guys, here's what I have: Stock bottom end 6.0, 241 heads, new ls7 lifters, new trays, stock rocker arms, custom comp cam. New Crank and cam gear, and new timing chain. I have stock pushrods (I know I need different ones with the cam-more on that in a second) ls6 intake, base tune by Mike Noris motor sports.
So, after starting with the new cam, ran great for 1:30 and I shut it off. Went to start it up after 30 minutes or so, and it started backfiring through the exhaust. Never did it in startup or while running, all the pushrods were straight, all valves checked out (applied air into the cylinders to check for leakage through intake or exhaust valves) Prior to this, the car started and ran fine.

I'll post both the old and new cam specs in comments. Thanks all!