As stated this LS2 based C6 has a radical CAM, FAST intake manifold, TB, and the changes listed in subject line

These type of mods esp when the trannie is a A6 and a radical CAM used that loses lots of low end vacuum very hard to tune and make it street driveable.

Stock flywheel horsepower of course is 402 and as shown in the results after we did the base custom tune

What is clear if you compare when engine is stock what the MAP is ( shown in red in graphs below) when looking at low end loads such as idle ( cells 17,18,19,20) is about in the 30s KPA but when narrow LSA CAMs are used you see how much MAP (vacuum) is lost as in this 2007 those same idle cells are in the 60s KPA. MAP is the inverse of vacuum so the higher MAP is the lower the vacuum is

This requires a lot more time and effort in custom tuning to get the results shown below