When converting a LS2/LS3 into a older C5 or just having a C6 it is a must to know which Crankshaft Position Sensor engine has and which one YOUR PCM was designed for

When looking towards the rear of C6 engine on the passenger side at the back, behind where the starter goes is the Crankshaft Position Sensor. What color is the actual sensor ?

Black..[you have a 24x crankshaft reluctor wheel] Part No 12560228

Grey ..[you have a 58x crankshaft reluctor wheel]
Such as shown below

A C5 PCM cannot understand the newer 58X wheel and you must change it to the older 24X to properly work with a C5 PCM.

Also the C5 PCM requires a using a 1x camshaft timing gear where LS2 is a 4X.