To me it sounds like you need a hotter plug or the tune is just way too rich.

The reason I asked about the head shims is that it's always possible there was a human error and there are too many shims installed in a new engine.


As for your exhaust pressure, the best way to tell is to look close at the connection to the header to engine and also header to exhaust. If you see any oily buildup you want to replace those exhaust gaskets.
Before the engine dies at idle is your idle nice and stable and it just drops really low and dies or does your idle bounce from low to high and then finally die?